APIs, Networking and Security
web application firewall
noun
Meaning
A firewall that sits in front of web applications and filters HTTP traffic to block common web attacks such as SQL injection and cross-site scripting.
Where you use it
Called a WAF, pronounced 'waff'. It can be a cloud service, an appliance or a module on the web server. Teams write WAF rules, run them first in detection mode and then switch to blocking mode. A WAF reduces risk but does not replace fixing the code.
Examples
We put the old booking site behind a web application firewall until it can be rewritten.
The web application firewall blocked the request because it looked like SQL injection.
Common phrases
WAF rule · cloud WAF · blocking mode · behind a WAF
More about this term →open port
noun
Meaning
A network port on a device that is accepting connections, which means a service is listening there and can be reached by others.
Where you use it
Found with port scans, for example with Nmap. Each open port is part of the attack surface, so unexpected ones, such as an exposed remote desktop or database port, are common findings. People say a port is open, closed or filtered.
Examples
The external scan found an open port 3389 on a test server.
Please close any open port that the application does not need.
Common phrases
port scan · close a port · listening service · exposed port
More about this term →digital signature
noun
Meaning
A cryptographic value attached to a message, document or file that proves who created it and shows that it has not been changed since it was signed.
Where you use it
Created with a private key and checked with the matching public key. Used for code signing, software updates, signed emails and legally recognised e-signatures. Security tools often trust signed files more, which is why stolen code-signing certificates are serious.
Examples
The update was rejected because its digital signature did not match the vendor's key.
All contracts in the portal are approved with a qualified digital signature.
Common phrases
verify a signature · code signing · signed binary · electronic signature
More about this term →ciphertext
noun
Meaning
Data after it has been encrypted, which looks like random characters and cannot be understood without the correct key. The readable original is called plaintext.
Where you use it
Mostly used in cryptography courses, standards and technical design documents, and almost always paired with plaintext: encryption turns plaintext into ciphertext, and decryption turns it back. 'Stored in plaintext' is a common, negative audit finding.
Examples
Even if the database is stolen, the card numbers are only ciphertext without the key.
The training tool shows the ciphertext and the plaintext side by side.
Common phrases
plaintext and ciphertext · stored in plaintext · cipher suite · block cipher
More about this term →threat hunting
noun
Meaning
Actively searching through systems and logs for signs of attackers who have not yet been detected by automated alerts, often starting from a hypothesis.
Where you use it
Done by experienced analysts, often at Tier 3. A hunt starts from a hypothesis ('an attacker may be using remote management tools'), uses SIEM and EDR data and ideally ends with new detection rules. People say they 'run a hunt'.
Examples
Our weekly threat hunting session found an old admin tool running on a file server.
After the advisory, we started threat hunting for the new IOCs across all endpoints.
Common phrases
threat hunting team · run a hunt · hypothesis-driven hunting · hunting query
More about this term →security control
noun
Meaning
Any safeguard, whether technical, administrative or physical, that reduces a security risk, such as a firewall, a policy, a training course or a locked door.
Where you use it
Standards such as ISO/IEC 27001 (Annex A) and NIST SP 800-53 are essentially lists of controls. Controls are designed, implemented and tested, and described as preventive, detective or corrective. Auditors check whether a control is in place and operating effectively.
Examples
MFA is our main security control against stolen passwords.
The auditor asked for evidence that the security control had worked all year.
Usage note
Here 'control' is a noun meaning a safeguard, not the verb 'to check'. Turkish auditors also use 'kontrol' in this sense.
Common phrases
implement a control · preventive control · detective control · compensating control · control framework
More about this term →GDPR
abbreviation
Meaning
General Data Protection Regulation: the European Union law, applied since May 2018, that sets rules for how organisations collect, use and protect personal data.
Where you use it
Said letter by letter. It can also apply to organisations outside the EU when they handle the data of people in the EU. Security teams meet it mostly through breach notification, which in many cases must reach the regulator within 72 hours of becoming aware.
Examples
Because EU customers were affected, we had to consider the GDPR notification deadline.
The data protection officer checks every new system against GDPR requirements.
Common phrases
GDPR compliance · breach notification · data protection officer · personal data · lawful basis
More about this term →hardening
noun
Meaning
The process of making a system more secure by removing unnecessary software and services, changing default settings and applying secure configurations.
Where you use it
The verb is 'harden': you harden a server, a container image or a laptop build. Teams follow hardening guides or benchmarks such as the CIS Benchmarks and check systems against them. A 'hardened image' is a standard, secure template.
Examples
Every new Linux server goes through hardening before it reaches production.
The hardening checklist disables SMBv1 and removes default accounts.
Common phrases
system hardening · harden a server · hardening guide · CIS Benchmarks · hardened image
More about this term →responsible disclosure
noun
Meaning
Reporting a vulnerability privately to the vendor or owner first and giving them reasonable time to fix it before any details are made public.
Where you use it
Today often called coordinated vulnerability disclosure (CVD). Researchers and vendors agree a deadline, often around 90 days. Companies publish a disclosure policy or a security.txt file that explains how to report issues.
Examples
Thanks to responsible disclosure, the patch was ready before the details went public.
Our responsible disclosure policy is linked from the website footer.
Common phrases
coordinated vulnerability disclosure · disclosure policy · disclosure deadline · full disclosure · security.txt
More about this term →bug bounty
noun
Meaning
A programme in which an organisation invites outside researchers to find and report vulnerabilities in its systems and pays rewards for valid reports.
Where you use it
Run directly or through platforms such as HackerOne and Bugcrowd. Each programme has a scope, rules and a payout table. Researchers submit a report, and the company triages it and decides the bounty.
Examples
We launched a private bug bounty with 50 invited researchers.
The bug bounty paid 5,000 dollars for the account takeover report.
Common phrases
bug bounty programme · bug bounty hunter · bounty payout · in scope · submit a report
More about this term →threat actor
noun
Meaning
A person or group responsible for a cyberattack or threat, such as a criminal gang, a state-backed group, a hacktivist or a malicious insider.
Where you use it
The neutral, professional word used in reports instead of 'hacker'. Threat intelligence firms track groups and give them names; well-resourced, long-term groups are called APTs (advanced persistent threats). Reports describe a threat actor's motives, tools and techniques.
Examples
The threat actor behind the campaign appears to be financially motivated.
We have no evidence linking this incident to a known threat actor.
Common phrases
financially motivated · state-sponsored group · APT group · attribute an attack
More about this term →spoofing
noun
Meaning
Faking an identity or source, such as an email sender, a phone number, a website or an IP address, so that a message or connection seems to come from someone trusted.
Where you use it
Used with many objects: email spoofing, caller ID spoofing, domain spoofing, ARP spoofing. The verb is 'spoof', and a spoofed email is one with a forged sender. Email protections such as SPF, DKIM and DMARC are designed against sender spoofing.
Examples
The invoice email used spoofing to look as if it came from our CEO.
Since we enforced DMARC, spoofing of our domain has dropped sharply.
Common phrases
email spoofing · spoofed sender · caller ID spoofing · domain spoofing · DMARC policy
More about this term →network
noun
Meaning
A group of computers, phones and other devices that are connected by cables or radio signals so that they can exchange data and share resources.
Where you use it
The most basic word in the field. Engineers design, build, manage and monitor networks, and talk about the office network, the guest network, the core network or the mobile network. As a verb, 'to network' usually means meeting people for your career, not connecting devices.
Examples
The printer isn't on the office network, so nobody can send print jobs to it.
We keep visitors on a separate guest network with internet access only.
Common phrases
office network · guest network · core network · network design · network engineer
More about this term →router
noun
Meaning
A device that connects different networks and decides, packet by packet, the best path for data to reach its destination, usually based on IP addresses.
Where you use it
Used in every networking context, from home internet to operator backbones. Engineers configure, reboot, replace and upgrade routers, and talk about edge routers, core routers and the router at a branch office. A switch works inside one network; a router moves traffic between networks.
Examples
The branch router lost its connection to headquarters at 9:40.
We need to replace the core routers before traffic doubles next year.
Usage note
Americans usually say /ˈraʊtər/, rhyming with 'outer'; many British speakers say /ˈruːtə/, like 'route' plus -er. Both are correct.
Common phrases
edge router · core router · configure a router · reboot the router · wireless router
More about this term →switch
noun
Meaning
A device with many ports that connects computers, phones, printers and other equipment inside the same local network and forwards each frame only to the port where its destination is.
Where you use it
A daily word in LAN work. Engineers talk about access switches on each floor, core switches in the server room, managed and unmanaged switches, and 24- or 48-port switches. The verb 'switch' (to change) also appears often, so context matters.
Examples
Plug the new phones into the access switch on the third floor.
We replaced the old unmanaged switch with a managed one so we can create VLANs.
Common phrases
access switch · core switch · managed switch · switch port · 48-port switch
More about this term →IP address
noun
Meaning
A unique numerical label given to every device on an IP network so that data can be sent to it, for example 192.168.1.20 in IPv4.
Where you use it
One of the first things checked in any troubleshooting. Devices get, release and renew IP addresses, and engineers assign them; they also distinguish public and private, static and dynamic addresses. People often just say 'IP': 'What's the IP of the printer?'
Examples
The laptop has an IP address from the wrong subnet, so it can't reach the file server.
Can you send me the IP address of the camera? I'll add it to the firewall rule.
Common phrases
assign an IP address · public IP address · IP address conflict · get an IP address · renew an IP address
More about this term →bandwidth
noun
Meaning
The maximum amount of data a connection can carry in a given time, usually measured in megabits or gigabits per second (Mbps, Gbps).
Where you use it
Used in capacity planning, sales and complaints alike. People buy, upgrade, use up and run out of bandwidth; a link may be short of bandwidth during backups. Bandwidth is the capacity of the pipe; throughput is how much data actually gets through.
Examples
Video calls are using most of the bandwidth on the branch link.
We upgraded the internet line from 100 Mbps to 1 Gbps because we kept running out of bandwidth.
Usage note
Mbps (megabits) and MBps (megabytes) are not the same: a byte is 8 bits, so 100 Mbps is about 12.5 megabytes per second.
Common phrases
increase bandwidth · bandwidth usage · high bandwidth · run out of bandwidth · bandwidth upgrade
More about this term →protocol
noun
Meaning
A set of agreed rules that defines how devices format, send, receive and check data, so that equipment from different vendors can talk to each other.
Where you use it
Used everywhere: routing protocols, network protocols, a protocol stack. Protocols are defined in standards such as RFCs and IEEE documents, and devices support, run or implement them. Many protocol names are acronyms ending in P: TCP, UDP, BGP, DHCP.
Examples
Both sites must run the same routing protocol, otherwise they won't exchange routes.
This old camera only supports outdated protocols, so we're keeping it on an isolated VLAN.
Common phrases
routing protocol · network protocol · protocol stack · support a protocol · run a protocol
More about this term →LAN
abbreviation
Meaning
Short for local area network: a network that connects devices in a limited area such as a home, an office floor or a single building.
Where you use it
Said as one word, 'lan'. Used for the internal side of a network: LAN ports, LAN cabling, the LAN interface of a router. It is the opposite of WAN. Wireless LAN (WLAN) means the Wi-Fi part of the local network.
Examples
All the PCs on the LAN can see the shared printer, but the laptops on Wi-Fi can't.
Connect the cable to one of the yellow LAN ports, not to the WAN port.
Common phrases
local area network · LAN port · wireless LAN · LAN cable · LAN segment
More about this term →WAN
abbreviation
Meaning
Short for wide area network: a network that links sites across cities or countries, usually over lines leased from a telecom operator or over the internet.
Where you use it
Said as one word, 'wan'. Companies talk about WAN links between branches, WAN costs and WAN optimisation. On a home router the WAN port is the one that goes to the internet; the other ports are LAN ports.
Examples
Each branch connects to the head office over a 200 Mbps WAN link.
The WAN port on the router is not getting an address from the ISP.
Common phrases
wide area network · WAN link · WAN port · WAN optimisation · WAN connection
More about this term →Wi-Fi
noun
Meaning
The common name for wireless local networks based on the IEEE 802.11 standards, which connect devices to a network by radio, mainly in the 2.4, 5 and 6 GHz bands.
Where you use it
Used by everyone, from users to engineers. People connect to and drop off Wi-Fi; engineers plan Wi-Fi coverage, upgrade to Wi-Fi 6 or Wi-Fi 7 and fix weak Wi-Fi in meeting rooms. Engineers often write WLAN in documentation and say 'wireless' in speech.
Examples
The Wi-Fi in the large meeting room drops whenever more than thirty people join.
Guests can use the Wi-Fi, but they can't reach any internal systems.
Usage note
Wi-Fi is a brand name, not an abbreviation; it does not officially stand for 'wireless fidelity'.
Common phrases
connect to Wi-Fi · Wi-Fi coverage · guest Wi-Fi · Wi-Fi signal · Wi-Fi password
More about this term →DHCP
abbreviation
Meaning
Short for Dynamic Host Configuration Protocol: a protocol that automatically gives devices an IP address, subnet mask, default gateway and DNS servers when they join a network.
Where you use it
Spelled out letter by letter. Engineers talk about the DHCP server, a DHCP pool or scope, DHCP leases and DHCP reservations. A typical problem is a pool that runs out of addresses, so new devices get no IP.
Examples
The guest Wi-Fi DHCP pool is full, so new phones aren't getting an address.
Set up a DHCP reservation for the printer so its address never changes.
Common phrases
DHCP server · DHCP pool · DHCP lease · DHCP reservation · DHCP relay
More about this term →default gateway
noun
Meaning
The router address that a device sends traffic to when the destination is outside its own subnet; without it, a device can only talk to its local network.
Where you use it
Checked early in almost every connectivity problem: 'Can you ping the default gateway?' Often shortened to 'gateway'. It is usually the first or last usable address of a subnet, and DHCP hands it out together with the IP address.
Examples
The PC has the wrong default gateway, so it can reach local printers but not the internet.
First ping the default gateway, then try an external address like 8.8.8.8.
Common phrases
set the default gateway · ping the default gateway · default gateway address · gateway of last resort
More about this term →packet
noun
Meaning
A small unit of data sent across a network, made of a header with addressing and control information and a payload that carries part of the actual content.
Where you use it
One of the most frequent words in the field. Packets are sent, received, forwarded, dropped, lost and captured. Strictly speaking, 'packet' is used at layer 3 (IP) and 'frame' at layer 2 (Ethernet), but in conversation people say 'packet' for both.
Examples
The firewall is dropping packets from that subnet.
Large files are split into thousands of packets that may take different paths.
Common phrases
drop packets · forward packets · packet header · packet size · packet loss
More about this term →port
noun
Meaning
Either a physical socket on a device where a network cable is plugged in, or a number from 0 to 65535 that identifies a particular service on a host, such as 443 for HTTPS.
Where you use it
Context tells you which meaning is used. On a switch, ports are up or down, enabled or shut down. In firewall and application work, ports are opened, closed, blocked or listened on: 'Is port 22 open?'
Examples
Port 12 on the second-floor switch is down; can someone check the cable?
The web server only listens on port 443, so plain HTTP requests fail.
Common phrases
open a port · port number · switch port · block a port · listen on a port
More about this term →TCP/IP
abbreviation
Meaning
The family of protocols that the internet and almost all modern networks are built on, named after its two best-known members, TCP and IP.
Where you use it
Used when talking about networking in general: the TCP/IP model, the TCP/IP stack, TCP/IP settings on a computer. The TCP/IP model is usually described with four layers and is the practical counterpart of the seven-layer OSI model.
Examples
Every device on the network needs correct TCP/IP settings: an address, a mask, a gateway and DNS.
The course starts with the TCP/IP model before moving on to routing.
Common phrases
TCP/IP model · TCP/IP stack · TCP/IP settings · TCP/IP suite
More about this term →Ethernet
noun
Meaning
The standard technology (IEEE 802.3) for wired local networks, which defines how devices send frames over copper or fibre cables at speeds from 10 Mbps up to hundreds of gigabits per second.
Where you use it
Used for wired connections in general: an Ethernet cable, an Ethernet port, Gigabit Ethernet. Copper Ethernet cables (Cat5e, Cat6) use RJ45 connectors and are normally limited to 100 metres per run.
Examples
For the video conference room, use Ethernet instead of Wi-Fi.
The new access points need Gigabit Ethernet ports with PoE.
Usage note
Ethernet is written with a capital E, and in English the first syllable has a long 'ee' sound: /ˈiːθənet/.
Common phrases
Ethernet cable · Ethernet port · Gigabit Ethernet · Ethernet switch · Ethernet frame
More about this term →configure
verb
Meaning
To set up a device or service by entering the settings it needs, such as addresses, passwords, VLANs and routing, so that it works the way the network requires.
Where you use it
A daily verb. Engineers configure interfaces, ports, VLANs and routing; the noun 'configuration' is usually shortened to 'config': the running config, a config backup. A misconfigured device is behind many outages.
Examples
I've configured the new switch, but I haven't saved the config yet.
Port 8 was configured in the wrong VLAN, so the phone couldn't get an address.
Common phrases
configure an interface · configure a VLAN · running configuration · misconfigured device · save the configuration
More about this term →MAC address
noun
Meaning
A hardware address, usually set in a network card at the factory, that identifies a device on a local network; it has 48 bits and is written as six pairs of hexadecimal digits.
Where you use it
'MAC' is said like the word 'mack'. Switches learn MAC addresses and store them in a MAC address table; engineers look up a MAC address to find which port a device is plugged into. Unlike an IP address, it only matters inside the local network.
Examples
Send me the MAC address of the new printer and I'll add a DHCP reservation.
The MAC address table shows the camera on port 17 of the second switch.
Common phrases
MAC address table · look up a MAC address · MAC filtering · learn a MAC address
More about this term →routing
noun
Meaning
The process of choosing the path that traffic takes from one network to another, carried out by routers using routes that are either entered by hand or learned from other routers.
Where you use it
Used in phrases like static routing, dynamic routing, routing protocols and routing issues. When traffic goes the wrong way or nowhere at all, engineers say it's a routing problem. Routing and switching together form the core of most networking jobs and certifications.
Examples
Routing between the two data centres is handled by BGP.
The VPN is up, but there's a routing issue: the remote side doesn't know how to reach our subnet.
Common phrases
dynamic routing · static routing · routing protocol · routing issue · routing and switching
More about this term →routing table
noun
Meaning
A list stored in a router or host that shows which networks it knows about and where to send packets for each one, such as the next router or an outgoing interface.
Where you use it
Engineers check or display the routing table when traffic doesn't arrive: 'Is the route in the routing table?' A route can be missing from, added to or removed from the table. The default route is used when no more specific route matches.
Examples
The 10.30.0.0/16 network isn't in the routing table, so the router drops that traffic.
After the OSPF change, the routing table on the core router has twice as many entries.
Common phrases
check the routing table · routing table entry · full routing table · default route
More about this term →VLAN
abbreviation
Meaning
Short for virtual LAN: a separate logical network created on a switch, so that devices plugged into the same hardware, for example staff PCs, guests and cameras, can be kept apart.
Where you use it
Said 'vee-lan'. Engineers create VLANs, assign ports to a VLAN, tag VLANs on trunk links and route between VLANs. VLANs are identified by numbers (1 to 4094 in the 802.1Q standard): 'Put this port in VLAN 20.'
Examples
Cameras are in VLAN 50, so they can't talk to staff laptops directly.
Can you move port 14 to the voice VLAN? A new IP phone is going there.
Common phrases
create a VLAN · voice VLAN · VLAN ID · assign a port to a VLAN · inter-VLAN routing
More about this term →access point
noun
Meaning
A device, usually mounted on a ceiling or wall, that sends and receives Wi-Fi signals and connects wireless devices to the wired network.
Where you use it
Often shortened to AP, said 'ay-pee'. Engineers install, mount, power and manage access points, often from a central wireless controller or a cloud dashboard. A home 'Wi-Fi router' combines a router and an access point in one box.
Examples
We need two more access points to cover the warehouse properly.
The access point in room 204 is offline; it has probably lost PoE power.
Common phrases
install an access point · wireless access point · ceiling-mounted access point · access point placement · wireless controller
More about this term →packet loss
noun
Meaning
A situation in which some packets sent across a network never reach their destination, usually shown as a percentage; it causes slow downloads, choppy calls and frozen video.
Where you use it
Reported in ping results and monitoring tools: '2% packet loss'. Engineers see, measure and investigate packet loss; typical causes are congestion, faulty cables, bad optics and wireless interference. Even 1% loss can make voice calls hard to follow.
Examples
We're seeing 5% packet loss on the link to Ankara, mostly in the evening.
The packet loss disappeared after we replaced the faulty patch cable.
Common phrases
packet loss rate · high packet loss · see packet loss · cause packet loss · intermittent packet loss
More about this term →OSI model
noun
Meaning
A reference model that splits network communication into seven layers, from the physical cable (layer 1) up to the application (layer 7), so that problems and technologies can be described clearly.
Where you use it
Used in training, interviews and everyday shorthand. Engineers say 'it's a layer 1 issue' for a cable problem, or talk about layer 2 and layer 3 switches. The seven layers are physical, data link, network, transport, session, presentation and application.
Examples
Let's go through the OSI model from the bottom: is the cable even plugged in?
In the interview they asked me to explain the seven layers of the OSI model.
Common phrases
OSI layer · layer 2 · layer 3 · OSI reference model · seven-layer model
More about this term →TCP
abbreviation
Meaning
Short for Transmission Control Protocol: a protocol that sets up a connection and makes sure data arrives complete and in the right order, resending anything that is lost.
Where you use it
Spelled out letter by letter. Web browsing, email and file transfers run over TCP. Engineers talk about TCP ports, TCP sessions, the three-way handshake (SYN, SYN-ACK, ACK) and TCP retransmissions when they analyse slow connections.
Examples
The capture shows a lot of TCP retransmissions, so packets are being lost somewhere.
SSH uses TCP port 22.
Usage note
TCP versus UDP is a classic interview question: TCP is reliable and connection-based; UDP is lighter and faster but does not check delivery.
Common phrases
TCP port · TCP connection · TCP handshake · TCP retransmission · TCP session
More about this term →UDP
abbreviation
Meaning
Short for User Datagram Protocol: a simple, fast protocol that sends data without setting up a connection and without checking whether it arrived; used for voice, video, DNS and gaming.
Where you use it
Spelled out letter by letter. Used when speed matters more than perfect delivery: a late voice packet is useless, so it is better to skip it than to resend it. Firewall rules must say whether a port is TCP or UDP.
Examples
DNS normally uses UDP port 53.
The firewall only allowed TCP, so the UDP traffic for the video calls was blocked.
Common phrases
UDP port · UDP traffic · UDP packet · UDP-based protocol
More about this term →IPv4
abbreviation
Meaning
Version 4 of the Internet Protocol, which uses 32-bit addresses written as four numbers from 0 to 255 separated by dots, such as 192.168.10.5; it allows about 4.3 billion addresses.
Where you use it
Said 'eye-pee-vee-four'. It is still the most common version in offices and homes. Because the supply of public IPv4 addresses has run out, operators rely on NAT and private address ranges, and companies buy or lease IPv4 blocks.
Examples
We only have eight public IPv4 addresses, so most services sit behind NAT.
The old devices support IPv4 only, so we can't switch it off yet.
Common phrases
IPv4 address · IPv4 exhaustion · IPv4 block · public IPv4 address
More about this term →IPv6
abbreviation
Meaning
Version 6 of the Internet Protocol, which uses 128-bit addresses written as groups of hexadecimal digits separated by colons, such as 2001:db8::1, giving an almost unlimited number of addresses.
Where you use it
Said 'eye-pee-vee-six'. Mobile operators and large content providers use it widely; many companies run IPv4 and IPv6 side by side, which is called dual stack. Engineers enable, deploy, roll out and troubleshoot IPv6.
Examples
Our mobile customers mostly reach the website over IPv6.
Before we roll out IPv6, we need to update the firewall rules as well.
Common phrases
IPv6 address · enable IPv6 · IPv6 rollout · dual stack · IPv6 prefix
More about this term →subnet mask
noun
Meaning
A number such as 255.255.255.0 that shows which part of an IPv4 address identifies the network and which part identifies the device; it can also be written as a prefix such as /24.
Where you use it
Entered together with the IP address and gateway, or handed out by DHCP. A wrong subnet mask is a classic configuration mistake: the device thinks local hosts are remote, or remote hosts are local. Engineers often just say 'the mask'.
Examples
The server was set up with a /16 subnet mask instead of /24, so it couldn't reach the other offices.
Check the subnet mask: 255.255.255.0 gives you 254 usable addresses.
Common phrases
wrong subnet mask · enter the subnet mask · /24 mask · mask and gateway
More about this term →NAT
abbreviation
Meaning
Short for network address translation: a method in which a router or firewall rewrites the addresses in packets, typically so that many devices with private addresses can share one public IP address.
Where you use it
Said like the word 'nat'. Engineers configure NAT rules, put servers behind NAT and troubleshoot applications that break behind NAT, such as some VoIP and VPN setups. Operators also use carrier-grade NAT (CGNAT) to share public addresses among many customers.
Examples
All 300 office PCs go out to the internet through NAT on a single public address.
The camera works locally but not from outside because there's no NAT rule for it.
Common phrases
NAT rule · behind NAT · static NAT · carrier-grade NAT · configure NAT
More about this term →static IP address
noun
Meaning
An IP address that is set by hand or permanently reserved for one device, so that it does not change, unlike a dynamic address handed out by DHCP.
Where you use it
Used for servers, printers, network devices and anything that other systems must always find at the same address. Businesses also buy a static IP address from their ISP to host a VPN or a server. Often shortened to 'static IP'.
Examples
Give the new NAS a static IP address outside the DHCP range.
We pay the ISP extra for a static IP address so the branch VPN can always find us.
Common phrases
assign a static IP address · static IP from the ISP · static vs dynamic IP · outside the DHCP range
More about this term →topology
noun
Meaning
The layout of a network: how its devices and links are arranged and connected, for example in a star, ring or mesh shape.
Where you use it
Used in design documents, diagrams and change plans. Engineers draw, document and redesign the network topology. Physical topology shows the actual cables; logical topology shows how traffic flows. Most office LANs use a star topology built around switches.
Examples
Please update the topology diagram after you add the new firewall.
The operator uses a ring topology, so traffic can go the other way round if one fibre is cut.
Common phrases
network topology · star topology · ring topology · mesh topology · topology diagram
More about this term →host
noun
Meaning
Any device on a network that has an IP address and sends or receives data, such as a computer, server, phone or printer.
Where you use it
Used in technical documents, commands and error messages: 'host unreachable', 'host not found', the number of hosts in a subnet. In server work 'host' can also mean the physical machine that runs virtual machines, so check the context.
Examples
A /26 subnet gives you 62 usable host addresses.
The scan found 140 active hosts on the office network.
Common phrases
host address · destination host unreachable · remote host · number of hosts
More about this term →SSID
abbreviation
Meaning
Short for service set identifier: the name of a Wi-Fi network, up to 32 characters long, that devices see in their list of available networks.
Where you use it
Spelled out letter by letter. Engineers create, broadcast, hide and rename SSIDs, and usually map each SSID to a VLAN: one for staff, one for guests, one for IoT devices. Too many SSIDs on the same access points waste airtime.
Examples
Visitors should join the 'Guest' SSID, not the corporate one.
We hid the SSID for the barcode scanners so it doesn't appear in people's Wi-Fi lists.
Common phrases
broadcast an SSID · hidden SSID · guest SSID · map an SSID to a VLAN
More about this term →traceroute
noun
Meaning
A diagnostic tool that lists every router a packet passes through on its way to a destination, with the delay to each one, so you can see where traffic slows down or stops.
Where you use it
Used as a noun and a verb: run a traceroute, traceroute to a server. On Windows the command is 'tracert'. It works by sending packets with increasing TTL values, so each hop reports back in turn. Engineers attach traceroute output to tickets they open with ISPs.
Examples
The traceroute stops at the ISP's second hop, so the problem isn't inside our network.
Please run a traceroute to the payment provider's server and paste the output into the ticket.
Common phrases
run a traceroute · traceroute output · traceroute to a host · tracert
More about this term →jitter
noun
Meaning
Variation in the delay of packets arriving over a network; when packets arrive at uneven intervals, voice and video calls become choppy or robotic.
Where you use it
Measured in milliseconds and watched closely for VoIP and video. Engineers measure, reduce and smooth out jitter, often with QoS and jitter buffers. As a rough guide, many voice systems aim to keep jitter below about 30 ms.
Examples
Latency is fine, but jitter on the branch link is making the audio sound robotic.
After we enabled QoS, jitter dropped from 45 ms to under 10 ms.
Common phrases
high jitter · jitter buffer · measure jitter · latency and jitter
More about this term →QoS
abbreviation
Meaning
Short for quality of service: a set of techniques that give important traffic, such as voice and video, priority over less urgent traffic when a link is busy.
Where you use it
Spelled out as 'Q-O-S' or said 'kwoss'. Engineers configure QoS policies, mark and classify traffic (for example with DSCP values) and apply QoS on WAN links. QoS cannot create bandwidth; it only decides who goes first when there isn't enough.
Examples
Without QoS, a large file upload can ruin every video call in the office.
We mark voice packets so the QoS policy on the WAN router puts them first.
Common phrases
QoS policy · configure QoS · QoS marking · apply QoS · end-to-end QoS
More about this term →BGP
abbreviation
Meaning
Short for Border Gateway Protocol: the routing protocol that networks on the internet use to exchange routes with each other, so that traffic can find its way between different operators and companies.
Where you use it
Spelled out letter by letter. Engineers set up BGP sessions with ISPs, advertise prefixes, filter routes and watch for BGP sessions going down. Each network is identified by an autonomous system number (ASN). Mistakes in BGP can make large parts of the internet unreachable.
Examples
We have BGP sessions with two ISPs, so if one fails, traffic moves to the other.
A wrong BGP announcement sent our traffic through another country for an hour.
Common phrases
BGP session · BGP peer · advertise a prefix · BGP routing · BGP neighbour
More about this term →OSPF
abbreviation
Meaning
Short for Open Shortest Path First: a routing protocol used inside one organisation's network, where routers share information about their links and each one calculates the best path itself.
Where you use it
Spelled out letter by letter. Engineers enable OSPF on interfaces, form neighbour relationships (adjacencies), design areas (area 0 is the backbone) and troubleshoot neighbours that get stuck. It is a link-state protocol and chooses paths by cost.
Examples
OSPF picked the slower path because nobody had adjusted the link costs.
The two routers aren't forming an OSPF adjacency; check that the area IDs match.
Common phrases
OSPF area · OSPF neighbour · OSPF adjacency · enable OSPF · OSPF cost
More about this term →static route
noun
Meaning
A route that an engineer enters into a router by hand, telling it exactly where to send traffic for a particular network, instead of letting a routing protocol learn it.
Where you use it
Engineers add, remove and redistribute static routes. They are simple and predictable, so small sites often use only a static default route pointing to the ISP. Their weakness is that they don't adapt automatically when a link fails.
Examples
Add a static route to 10.50.0.0/16 via the VPN firewall.
Someone left an old static route in place, so traffic kept going to the closed office.
Common phrases
add a static route · static default route · floating static route · remove a static route
More about this term →trunk port
noun
Meaning
A switch port that carries traffic for several VLANs over one link, adding a tag to each frame so the device at the other end knows which VLAN it belongs to.
Where you use it
Used for links between switches and to routers, firewalls and virtualisation hosts. The opposite is an access port, which carries a single VLAN for an end device. 'Trunk' is mostly Cisco wording; other vendors often say 'tagged port'. Tagging follows the IEEE 802.1Q standard.
Examples
VLAN 30 isn't allowed on the trunk port to the second floor, so those phones can't register.
Configure the uplink as a trunk port and allow VLANs 10, 20 and 30.
Common phrases
configure a trunk port · trunk link · allowed VLANs · access port · native VLAN
More about this term →spanning tree protocol
noun
Meaning
A protocol that stops switches from forming loops by blocking extra paths between them, and opens a blocked path again if an active link fails.
Where you use it
Usually called STP; faster versions are RSTP and MSTP. Engineers set the root bridge, check port states (forwarding, blocking) and investigate spanning tree events after a network slowdown. Without it, a single loop can cause a broadcast storm that brings down a whole LAN.
Examples
Someone plugged both ends of a cable into the same switch, but spanning tree protocol blocked the loop.
We moved from classic spanning tree protocol to RSTP to recover faster after link failures.
Common phrases
spanning tree · root bridge · blocking port · rapid spanning tree · spanning tree loop
More about this term →maintenance window
noun
Meaning
An agreed period, usually at night or at the weekend, when engineers are allowed to make changes that may interrupt service, such as software upgrades and hardware swaps.
Where you use it
Used in change management and customer notices. Teams schedule, request, announce and extend maintenance windows; work must finish, or be rolled back, before the window closes. Operators notify customers about the maintenance window in advance.
Examples
The core router upgrade is scheduled for Saturday's maintenance window, 01:00 to 05:00.
We ran out of time in the maintenance window, so we rolled back the change.
Common phrases
schedule a maintenance window · overnight maintenance window · within the maintenance window · extend the maintenance window
More about this term →roaming
noun
Meaning
Using a mobile network other than your own operator's, usually abroad; in Wi-Fi, moving from one access point to another without losing the connection.
Where you use it
Mobile operators sign roaming agreements and charge roaming fees, and customers turn data roaming on or off. Wi-Fi engineers tune roaming so that phones and laptops switch smoothly to a closer access point as people walk around a building.
Examples
Turn off data roaming before you land, or the bill could be very high.
Calls drop when people walk to the warehouse, so we need to look at Wi-Fi roaming.
Common phrases
data roaming · roaming agreement · roaming charges · international roaming · seamless roaming
More about this term →packet capture
noun
Meaning
A recording of the actual packets passing through a network interface, saved to a file so that engineers can analyse exactly what was sent and received.
Where you use it
Used when other troubleshooting has not found the cause. Engineers take, open and analyse a packet capture, usually with tools such as Wireshark or tcpdump, and the file is often a .pcap. In speech people say 'grab a capture' or 'take a pcap'.
Examples
Can you take a packet capture on the firewall while the user tries to log in?
The packet capture showed the server was resetting the connections, so it wasn't a network problem.
Common phrases
take a packet capture · analyse a packet capture · pcap file · capture filter
More about this term →SNMP
abbreviation
Meaning
Short for Simple Network Management Protocol: a protocol that lets monitoring systems collect information such as traffic, errors and temperature from network devices, and lets devices send alerts.
Where you use it
Spelled out letter by letter. Monitoring tools poll devices with SNMP, and devices send SNMP traps when something happens, such as a link going down. Versions 1 and 2c use a shared 'community string'; SNMPv3 adds authentication and encryption and is the safer choice.
Examples
The new switches aren't in the monitoring system yet because SNMP isn't configured.
We received an SNMP trap saying the fan in rack 4 has failed.
Common phrases
SNMP trap · SNMP polling · community string · SNMPv3 · enable SNMP
More about this term →network monitoring
noun
Meaning
Continuously checking the health and performance of network devices and links, such as availability, traffic, errors and latency, and alerting engineers when something goes wrong.
Where you use it
Used for both the activity and the tools. Engineers set up network monitoring, add devices to it, set thresholds and respond to alerts. Good monitoring means the NOC notices an outage before the customers call.
Examples
Network monitoring flagged high CPU on the core router twenty minutes before the outage.
Every new device has to be added to network monitoring before it goes live.
Common phrases
network monitoring tool · monitoring dashboard · set up monitoring · monitoring alert · proactive monitoring
More about this term →congestion
noun
Meaning
A situation in which more traffic is trying to cross a link or device than it can handle, so packets are queued or dropped and everything slows down.
Where you use it
Used in performance discussions, capacity planning and operator reports. Congestion builds up at peak hours, causes latency and packet loss, and is managed with QoS and capacity upgrades. Operators talk about evening congestion, when everyone is streaming video.
Examples
Congestion on the uplink between 8 and 11 p.m. is causing the packet loss.
We added a second 10G link to relieve congestion between the data centres.
Common phrases
network congestion · peak-hour congestion · relieve congestion · congestion control · link congestion
More about this term →round-trip time
noun
Meaning
The time it takes for a packet to travel from a source to a destination and for the reply to come back, usually shown in milliseconds; ping reports this value.
Where you use it
Often shortened to RTT. Used in performance tests, SLA reports and application tuning. Engineers compare average, minimum and maximum round-trip times. Distance matters: light in fibre needs about 5 ms to travel 1,000 km one way.
Examples
The round-trip time from Istanbul to London is usually around 50 to 60 ms.
The round-trip time jumps to 300 ms every time the backup runs.
Common phrases
average round-trip time · measure the round-trip time · high round-trip time · RTT
More about this term →ACL
abbreviation
Meaning
Short for access control list: an ordered list of rules on a router, switch or firewall that permits or denies traffic based on things like source, destination, protocol and port.
Where you use it
Spelled out letter by letter. Engineers write ACLs, apply them to interfaces in the inbound or outbound direction and keep them up to date. Rules are checked from top to bottom and the first match wins; on many devices an invisible 'deny all' rule sits at the end, so anything not explicitly allowed is dropped.
Examples
The new ACL blocks traffic from the guest VLAN to the server subnet.
Monitoring stopped working after the change because the ACL didn't permit SNMP.
Common phrases
apply an ACL · inbound ACL · ACL entry · permit and deny rules · implicit deny
More about this term →port forwarding
noun
Meaning
A NAT rule that sends traffic arriving on a public IP address and port to a specific device and port inside a private network, so that an internal service can be reached from outside.
Where you use it
Common in small offices and home setups: engineers set up, add or remove port forwarding on the router or firewall for cameras, game servers or remote access. Opening ports to the internet carries security risks, so many companies prefer a VPN.
Examples
We set up port forwarding so that port 8443 on the public address goes to the camera recorder.
Remove the old port forwarding rule for RDP; it's a security risk.
Common phrases
set up port forwarding · port forwarding rule · forward a port · open a port
More about this term →DMZ
abbreviation
Meaning
Short for demilitarised zone: a separate network segment between the internet and the internal network, where public-facing servers such as web or mail servers are placed.
Where you use it
Spelled out letter by letter. Servers are placed in or moved to the DMZ, so that if one is compromised, an attacker still has to get past the firewall to reach internal systems. Firewall rules usually allow traffic from the internet into the DMZ but strictly limit traffic from the DMZ inwards.
Examples
The new web server will sit in the DMZ, not on the internal network.
Only port 443 is open from the internet to the DMZ.
Common phrases
DMZ network · place a server in the DMZ · DMZ segment · DMZ firewall rules
More about this term →MPLS
abbreviation
Meaning
Short for Multiprotocol Label Switching: a technique used in operator networks that forwards traffic using short labels instead of full IP lookups; it is widely sold to companies as a private WAN service.
Where you use it
Spelled out letter by letter. Companies buy MPLS circuits or an MPLS VPN from a carrier to connect their branches privately, with QoS and an SLA. Many are now moving part of that traffic to SD-WAN over cheaper internet links.
Examples
All 60 branches connect to the data centre over the carrier's MPLS network.
The MPLS contract ends next year, so we're evaluating SD-WAN.
Common phrases
MPLS network · MPLS circuit · MPLS VPN · MPLS label
More about this term →SD-WAN
abbreviation
Meaning
Short for software-defined wide area network: an approach that manages a company's WAN links centrally through software and sends each application over the best available link, such as internet, 4G or MPLS.
Where you use it
Said 'S-D-wan'. Companies deploy, migrate to and roll out SD-WAN; engineers set application policies, for example sending video calls over the link with the lowest latency. Branch devices are often installed with zero-touch provisioning: someone plugs them in and they download their own configuration.
Examples
Since we moved to SD-WAN, a single broken line no longer stops sales at a branch.
The SD-WAN policy sends voice traffic over the fibre line and backups over 4G.
Common phrases
SD-WAN deployment · SD-WAN appliance · migrate to SD-WAN · SD-WAN policy
More about this term →hop
noun
Meaning
One step in the path of a packet, from one router to the next; the number of hops shows how many routers a packet passes through to reach its destination.
Where you use it
Used when reading traceroute output and configuring routing: hop count, next hop, 'the third hop is slow'. Each hop reduces the packet's TTL (time to live) by one, and the packet is discarded when it reaches zero, which stops packets from looping forever.
Examples
Latency jumps at the fifth hop, which is inside the ISP's network.
Set the next hop for this static route to 10.0.0.1.
Common phrases
next hop · hop count · first hop · multi-hop
More about this term →ARP
abbreviation
Meaning
Short for Address Resolution Protocol: the protocol a device uses on a local network to find the MAC address that belongs to a known IPv4 address.
Where you use it
Usually said as a word, 'arp'. Devices send ARP requests and keep the answers in an ARP table, also called the ARP cache. Engineers check the ARP table to see which IP address belongs to which MAC address. IPv6 uses a different mechanism, Neighbor Discovery, instead of ARP.
Examples
The router's ARP table shows two devices using the same IP address.
Clear the ARP cache on the firewall after you replace the server.
Common phrases
ARP table · ARP request · ARP cache · clear the ARP cache · gratuitous ARP
More about this term →ICMP
abbreviation
Meaning
Short for Internet Control Message Protocol: a protocol that network devices use to send error and status messages, such as 'destination unreachable'; ping and traceroute rely on it.
Where you use it
Spelled out letter by letter. Firewalls often block ICMP for security reasons, which makes ping fail even when a host is working. Blocking all ICMP can also break functions such as path MTU discovery, so most teams allow the important message types.
Examples
The server is up, but it doesn't answer ping because ICMP is blocked on its firewall.
The router sent back an ICMP 'destination unreachable' message.
Common phrases
ICMP echo request · block ICMP · ICMP message · ICMP unreachable
More about this term →broadcast
noun
Meaning
A message sent to every device on the local network segment at once, instead of to a single address; routers do not forward broadcasts to other networks.
Where you use it
Used as a noun and an adjective: broadcast traffic, broadcast address, broadcast domain. DHCP and ARP rely on broadcasts. Engineers keep broadcast domains small with VLANs, because too many broadcasts, or a broadcast storm caused by a loop, can slow down or stop a LAN.
Examples
The loop caused a broadcast storm that took down the whole floor.
Each VLAN is its own broadcast domain, so broadcasts from the cameras don't reach the PCs.
Common phrases
broadcast domain · broadcast storm · broadcast address · broadcast traffic
More about this term →CIDR
abbreviation
Meaning
Short for Classless Inter-Domain Routing: the system of writing an IP network as an address plus a prefix length, such as 192.168.0.0/22, which replaced the old fixed address classes.
Where you use it
Usually said like the drink 'cider'. Engineers use CIDR notation everywhere: in firewall rules, routing tables and cloud network settings. The number after the slash shows how many bits belong to the network: a /24 has 256 addresses, a /30 has four.
Examples
Write the subnet in CIDR notation, for example 10.10.0.0/16, not with the full mask.
The cloud team asked for a /20 CIDR block for the new environment.
Common phrases
CIDR notation · CIDR block · CIDR range · prefix length
More about this term →private IP address
noun
Meaning
An IP address from the ranges reserved for internal networks, such as 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16, which cannot be routed on the public internet.
Where you use it
Used every day in office and home networks. Devices with private IP addresses reach the internet through NAT. Problems appear when two companies, or a home and an office, use the same private range and are joined by a VPN, because the addresses overlap.
Examples
The printer has a private IP address, so you can't reach it from outside without the VPN.
Both offices use 192.168.1.0/24 as their private IP address range, so the VPN between them can't route properly.
Common phrases
private IP range · private vs public IP · RFC 1918 address · overlapping address ranges
More about this term →NOC
abbreviation
Meaning
Short for network operations centre: the team and room, often staffed 24/7, that monitors a network, responds to alarms and coordinates the repair of faults and outages.
Where you use it
Said like the word 'knock'. Operators, ISPs and large companies run a NOC; engineers call the NOC, escalate issues to it or get paged by it. NOC staff open tickets, contact field teams and post status updates. Its security counterpart is the SOC.
Examples
The NOC noticed the fibre cut within two minutes and sent a field team.
If the link is still down after 30 minutes, escalate to the NOC.
Common phrases
NOC engineer · 24/7 NOC · escalate to the NOC · NOC dashboard · call the NOC
More about this term →multiplayer
adjective
Meaning
Describes a game or mode in which several people play together or against each other, online or on the same device. As a noun, it means the multiplayer part of a game.
Where you use it
The opposite is single-player. People talk about online multiplayer, local multiplayer on one screen or console, and co-op, where players work together. Multiplayer adds a lot of networking work, so teams decide early whether a game needs it.
Examples
Adding multiplayer late in development almost always causes problems.
The game has a 20-hour campaign and a four-player online multiplayer mode.
Common phrases
online multiplayer · local multiplayer · multiplayer mode · co-op multiplayer · multiplayer server
More about this term →dedicated server
noun
Meaning
A computer, usually in a data center, that runs only the game server and the shared game world, while players connect to it instead of one player hosting the match.
Where you use it
Competitive online games usually use dedicated servers because they are fairer and harder to cheat on, but they cost money to run. The alternatives are listen servers, where one player hosts, and peer-to-peer connections.
Examples
Dedicated server costs will be one of our biggest monthly expenses.
Ranked matches run on dedicated servers; casual matches are hosted by players.
Common phrases
run dedicated servers · dedicated server costs · host a dedicated server · server region
More about this term →netcode
noun
Meaning
The networking code of an online game that sends game data between players and servers and keeps everyone's view of the match in sync despite delays.
Where you use it
Players and reviewers judge netcode as good or bad, especially in fighting games and shooters. Developers discuss rollback netcode, delay-based netcode and how much data to send per tick.
Examples
The game is fun, but the netcode makes long-distance matches unplayable.
Switching to rollback netcode was the biggest improvement after launch.
Common phrases
rollback netcode · bad netcode · netcode programmer · improve the netcode
More about this term →matchmaking
noun
Meaning
The system that puts online players into matches with or against each other, based on things like skill level, region and connection quality.
Where you use it
Players complain about long matchmaking times or unfair matches. Skill-based matchmaking, often shortened to SBMM, uses a hidden rating. Developers tune the trade-off between match quality and waiting time.
Examples
Matchmaking takes over five minutes at night because there aren't enough players.
We widen the skill range in matchmaking after the first 60 seconds.
Common phrases
skill-based matchmaking · matchmaking time · matchmaking queue · ranked matchmaking
More about this term →lag
noun
Meaning
A noticeable delay between a player's action and the game's reaction, usually caused by a slow or unstable network connection, which makes the game feel jumpy.
Where you use it
An informal word used by players, community managers and developers. Also a verb: the game lags. Players say a server is laggy, and a lag spike is a short burst of very bad lag.
Examples
Players in the Middle East report lag every evening after 9 p.m.
That wasn't lag; the hitbox on that attack is just too big.
Usage note
Input lag is different: it is the delay between pressing a button and seeing the result on screen, even when you play offline.
Common phrases
lag spike · input lag · laggy server · cause lag · lag compensation
More about this term →tick rate
noun
Meaning
How many times per second a game server updates the game state and sends it to players, measured in hertz. A higher tick rate makes online play more precise.
Where you use it
Competitive shooters advertise 64 Hz or 128 Hz servers, and each single update is called a tick. A higher tick rate costs more server power and bandwidth, so teams choose a rate for each game mode.
Examples
We raised the tick rate to 60 for ranked matches only.
With a low tick rate, players get hit after they've already ducked behind cover.
Common phrases
server tick rate · 128-tick server · raise the tick rate · per tick
More about this term →lobby
noun
Meaning
A virtual waiting area where players gather before an online match starts, to form teams, choose characters or settings, and wait for others to join.
Where you use it
Players create, host, join and leave lobbies; a private lobby needs an invite or a code. Developers talk about lobby systems and the lobby services offered by platforms and backend providers.
Examples
Players can invite friends to a private lobby with a six-letter code.
The lobby closes when the host leaves, which kicks everyone out.
Common phrases
private lobby · join a lobby · lobby host · lobby system · pre-game lobby
More about this term →client-side prediction
noun
Meaning
A netcode technique in which the player's own device shows the result of their input immediately, before the server confirms it, and corrects it later if the server disagrees.
Where you use it
Used to hide latency so that movement feels instant. When a prediction is wrong, the correction is called reconciliation, and players may see rubber-banding: their character snaps back to an earlier position.
Examples
Without client-side prediction, every step would feel 100 ms late.
The rubber-banding happens on slopes, where our client-side prediction disagrees with the server.
Common phrases
server reconciliation · rubber-banding · lag compensation · input prediction
More about this term →authoritative server
noun
Meaning
A server that has the final say on what happens in an online game: players send their inputs, and the server decides the real results, which makes cheating harder.
Where you use it
Network programmers say a game is server-authoritative, or that the server is authoritative over health or position. The basic rule is 'never trust the client'. It is usually combined with client-side prediction to hide latency.
Examples
With an authoritative server, a hacked client can't just give itself more gold.
Damage is always calculated on the authoritative server, never on the player's machine.
Common phrases
server-authoritative · never trust the client · authoritative over · server validation
More about this term →Release and Maintenance
deploy
verb
Meaning
To put a new version of software onto servers or devices so that it starts running there, for example in a test environment or for real users.
Where you use it
Very common in daily work: 'deploy to staging', 'deploy to production', 'Do we deploy on Fridays?' The noun is 'deployment', though developers also say 'a deploy' informally.
Examples
We deploy to production every Tuesday and Thursday.
Can you deploy my branch to staging so the designer can check it?
The deployment failed because a database migration timed out.
Usage note
'Deploy' is a verb; the standard noun is 'deployment'. 'A deploy' is common in speech but sounds informal in written reports.
Common phrases
deploy to production · deploy to staging · deploy a fix · failed deployment · automated deployment
More about this term →release
noun
Meaning
A version of a product that is made available to users, or the act of making it available. Also a verb: to release a new version.
Where you use it
Teams plan, prepare, cut and ship releases. You hear 'release notes', 'release date', 'release branch' and 'the next release'. Mobile teams also talk about submitting a release to the app stores.
Examples
This fix will go out in the next release.
Can you add the API changes to the release notes?
We released version 3.2 on Monday without any issues.
Common phrases
the next release · release notes · cut a release · release date · release branch
More about this term →production
noun
Meaning
The live environment where real users use the software, as opposed to development or test environments.
Where you use it
Usually shortened to 'prod'. People say 'in production', 'deploy to production', 'a production issue' and 'production data'. A problem 'in prod' is always taken seriously.
Examples
The bug only happens in production, not on my local machine.
Please don't run that migration on production until we have a backup.
Usage note
Turkish 'canlıya almak' is 'deploy to production', 'go live' or 'push to prod' in English, never 'take to live'.
Common phrases
in production · deploy to production · production issue · production environment · go to production
More about this term →build
noun
Meaning
The process of turning source code into a program or package that can run, or the result of that process. Also a verb: to build the project.
Where you use it
In CI, 'the build' compiles the code and runs the tests on every push. People say 'the build is green' or 'red', 'the build is broken', 'Who broke the build?' and 'a new build is ready for testing'.
Examples
The build is red again. Somebody pushed a failing test.
QA is testing the Android build from this morning.
It takes about twelve minutes to build the whole project.
Usage note
Turkish 'build almak' is not 'take a build' in English. Say 'run a build', 'make a build' or 'trigger a build'.
Common phrases
the build is broken · break the build · build pipeline · nightly build · a new build
More about this term →ship
verb
Meaning
To release a product or feature so that real users can use it. The word is borrowed from the idea of sending goods to customers.
Where you use it
Informal but very common in product teams and start-ups: 'We shipped it last week', 'ship fast', 'Ship it!' It puts the focus on getting work into users' hands, not just on finishing the code.
Examples
We shipped dark mode on Tuesday, and the feedback has been great.
It's not perfect, but it's good enough to ship.
Common phrases
ship a feature · ship to production · ship fast · ready to ship · ship it
More about this term →documentation
noun
Meaning
Written material that explains how software works and how to use, set up or change it, such as guides, API references and README files.
Where you use it
Usually shortened to 'docs'. Developers read, write, update and link to documentation. Common complaints include 'The docs are out of date' and 'It's not in the documentation.'
Examples
According to the documentation, the token expires after one hour.
Please update the documentation when you change the config options.
Usage note
'Documentation' is uncountable: say 'the documentation' or 'the docs', not 'documentations'.
Common phrases
read the documentation · update the documentation · API documentation · out-of-date documentation · technical documentation
More about this term →CI/CD
abbreviation
Meaning
Short for continuous integration and continuous delivery (or deployment): automatically building and testing every change, then releasing it quickly and safely.
Where you use it
Teams set up and maintain a 'CI/CD pipeline' with tools such as GitHub Actions, GitLab CI or Jenkins. People often say just 'CI': 'CI is failing', 'Wait for CI to pass.'
Examples
Our CI/CD pipeline runs the tests and deploys to staging on every merge.
Setting up CI/CD early saved us a lot of manual release work.
Common phrases
CI/CD pipeline · set up CI/CD · CI is green · wait for CI
More about this term →hotfix
noun
Meaning
An urgent fix for a serious problem in production, released quickly outside the normal release schedule.
Where you use it
Teams prepare, ship and deploy hotfixes, often from a separate 'hotfix branch'. A hotfix is usually small, focused on one issue and reviewed quickly but carefully.
Examples
We pushed a hotfix at midnight because users couldn't log in.
Create the hotfix branch from the release tag, not from main.
Common phrases
deploy a hotfix · hotfix branch · emergency hotfix · ship a hotfix
More about this term →roll back
phrasal verb
Meaning
To return a system to an earlier working version after a release or change causes problems.
Where you use it
Often said under pressure during incidents: 'Roll it back!', 'We rolled back the deployment.' The noun is one word, 'rollback', as in 'a rollback plan'. Database changes can be harder to roll back than code.
Examples
Error rates doubled after the release, so we rolled back within ten minutes.
Every deployment needs a rollback plan.
Usage note
The verb is two words ('roll back'), while the noun and adjective are one word ('a rollback', 'rollback plan').
Common phrases
roll back a release · roll back the deployment · rollback plan · automatic rollback
More about this term →staging
noun
Meaning
An environment set up to be as close as possible to production, where a team checks a release one last time before real users get it.
Where you use it
Short for 'staging environment' or 'staging server'. People say 'deploy to staging', 'test it on staging' and 'It works on staging but not in prod.'
Examples
The new checkout is on staging. Can the product team take a look today?
Staging uses a copy of production data with personal details removed.
Usage note
In Git, 'staging' has another meaning: choosing which changes go into the next commit (the 'staging area', filled with git add).
Common phrases
deploy to staging · staging environment · on staging · staging server
More about this term →legacy code
noun
Meaning
Old code that is still in use, often written by people who have left, with little documentation or few tests, so it feels risky to change.
Where you use it
Developers maintain, modernize, migrate and sometimes fear legacy code. 'Legacy system' and 'legacy app' are common too. The word can be neutral or slightly negative, depending on the tone.
Examples
Nobody wants to touch the legacy code in the billing module because it has no tests.
Our plan is to wrap the legacy code in an API and replace it piece by piece.
Common phrases
maintain legacy code · legacy system · legacy codebase · migrate legacy code
More about this term →deprecate
verb
Meaning
To officially mark a feature, function or API as outdated and not recommended, usually as a warning that it will be removed in a later version.
Where you use it
Usually passive: 'This method is deprecated', 'v1 of the API was deprecated last year.' Teams publish deprecation notices and timelines so that users have time to switch. You also see 'deprecation warning' in logs.
Examples
This function is deprecated. Use formatDate() from the new utils module instead.
We'll deprecate the old endpoint in March and remove it in September.
Usage note
Don't confuse it with 'depreciate', which means to lose value over time, as money, cars or equipment do.
Common phrases
deprecated API · deprecation warning · deprecated in favor of · deprecate an endpoint
More about this term →release notes
noun
Meaning
A short document published with a new version of software that lists new features, bug fixes, known issues and other changes users should know about.
Where you use it
Written for users or customers, so the language is simpler than in a changelog. Always plural. Common phrases: 'write the release notes', 'see the release notes', 'mentioned in the release notes'. Reading them before an upgrade helps you spot breaking changes.
Examples
Can you write the release notes for version 3.2 in plain language for our customers?
According to the release notes, the old login API will be removed next year.
Common phrases
write release notes · publish release notes · according to the release notes · release notes for version
More about this term →patch
noun
Meaning
A small update that fixes bugs or security problems in software without adding big new features. It is also a verb: to patch a system.
Where you use it
Teams release, apply or roll out a patch. 'Security patch' and 'patch release' are common. In semantic versioning, going from 1.4.2 to 1.4.3 is a patch version. As a verb: 'We patched the vulnerability within a day.'
Examples
Apply the security patch to all servers before Friday.
Version 2.1.1 is a patch release; it only fixes the export bug.
Common phrases
security patch · apply a patch · patch release · patch a vulnerability
More about this term →upgrade
verb
Meaning
To move to a newer, usually better version of software, a library or a tool, for example from Python 3.10 to Python 3.12.
Where you use it
You upgrade a dependency, a framework or a database 'to version X'. An upgrade can be a big project when there are breaking changes. The noun is stressed on the first syllable (an UPgrade), the verb often on the second (to upGRADE). The opposite is downgrade.
Examples
We need to upgrade React before we can use the new compiler.
The database upgrade is planned for Sunday night, when traffic is low.
Usage note
'Update' often means a smaller change within the same version line, while 'upgrade' suggests moving to a newer major or minor version.
Common phrases
upgrade to version · upgrade a dependency · major upgrade · upgrade path
More about this term →go live
phrase
Meaning
To become available to real users for the first time, for example when a new system, feature or website is launched in production.
Where you use it
Used as a verb ('the new app goes live on Monday') and, with a hyphen, as a noun or adjective ('the go-live date', 'a go-live checklist'). Very common in project plans and status updates. Similar to 'launch'.
Examples
The new payment system goes live next Tuesday at 6 a.m.
We moved the go-live date because the security review isn't finished.
Common phrases
go-live date · go live in production · go-live checklist · before we go live
More about this term →changelog
noun
Meaning
A file or page that lists the notable changes in each version of a project, usually with the newest version first. It is often named CHANGELOG.md.
Where you use it
More technical and detailed than release notes. A common format groups entries under Added, Changed, Deprecated, Removed, Fixed and Security. Reviewers may ask you to add an entry to the changelog in your pull request.
Examples
Please add a line to the changelog under 'Fixed' before we merge.
I checked the changelog, and version 5 removes the old config format.
Common phrases
update the changelog · changelog entry · keep a changelog · CHANGELOG.md
More about this term →semantic versioning
noun
Meaning
A version-numbering rule with three parts, MAJOR.MINOR.PATCH: the first number changes for breaking changes, the second for new features and the third for bug fixes.
Where you use it
Often shortened to SemVer. For example, going from 2.3.1 to 3.0.0 tells users to expect breaking changes, while 2.3.2 should be a safe update. Package managers use these rules for version ranges such as ^2.3.0.
Examples
We follow semantic versioning, so removing that endpoint means we have to release 4.0.0.
Not every library follows semantic versioning strictly, so read the changelog before upgrading.
Common phrases
follow semantic versioning · SemVer · major version · minor version · patch version
More about this term →code freeze
noun
Meaning
A period before a release, or during busy times such as holidays, when no new code changes may be merged except critical fixes.
Where you use it
Teams announce 'We're in code freeze until Monday' or 'Code freeze starts Thursday at noon'. Online shops often have a code freeze around big sale days. A 'feature freeze' is lighter: no new features, but bug fixes are still allowed.
Examples
Code freeze starts on Wednesday, so get your pull requests merged before then.
During the Black Friday code freeze, only the on-call engineer can deploy.
Common phrases
code freeze starts · during the code freeze · feature freeze · lift the code freeze
More about this term →