Software Engineering Vocabulary: 1,000 Key English Terms

readable

adjective

Meaning

Easy for another person to read and understand quickly, thanks to clear names, a simple structure and short functions.

Where you use it

One of the most common words in code reviews: 'more readable', 'hard to read', 'for readability'. Readable code is usually preferred over clever code. The noun is readability.

Examples

1. Splitting this into two functions would make it much more readable.

2. I renamed a few variables for readability; the logic is unchanged.

Common phrases

more readable · readable code · for readability · improve readability

best practice

noun

Meaning

A way of working that experienced people widely agree gives the best results, such as writing tests, reviewing code and never storing passwords in plain text.

Where you use it

Often plural: 'follow best practices', 'security best practices', 'it's best practice to…'. In reviews, it gently explains why a change is needed. Be ready to give the reason, because 'best practice' alone can sound like an excuse.

Examples

1. It's best practice to validate input on the server, even if the form already checks it.

2. We wrote a short guide on API best practices for new team members.

Common phrases

follow best practices · security best practices · industry best practice · it's best practice to

clean code

noun

Meaning

Code that is simple, clearly named, well organized and easy for others to read, test and change, rather than code that only works.

Where you use it

Popularized by Robert C. Martin's 2008 book 'Clean Code'. Teams talk about writing clean code and about principles such as small functions and meaningful names. Some developers warn against following such rules too strictly.

Examples

1. Clean code isn't about being clever; it's about the next person understanding it quickly.

2. Our team's clean code guidelines say that a function should do one thing.

Common phrases

write clean code · clean code principles · keep the code clean · clean code guidelines

maintainable

adjective

Meaning

Easy to understand, fix and extend over a long time, even by developers who did not write the original code.

Where you use it

A key goal in architecture and code review: 'Is this maintainable?' The noun is maintainability. Code with tests, a clear structure and few hidden dependencies is more maintainable. The opposite, 'unmaintainable', is a strong criticism.

Examples

1. It works, but it isn't maintainable: nobody else will understand these regex rules.

2. We chose the boring framework because it keeps the code more maintainable.

Common phrases

maintainable code · more maintainable · long-term maintainability · hard to maintain

naming convention

noun

Meaning

An agreed set of rules for how to name things in code, such as variables, files and branches, so that names look consistent across a project.

Where you use it

Examples are camelCase for variables in JavaScript, snake_case in Python and PascalCase for class names. Reviewers point out names that 'don't follow our naming convention'. Many conventions are enforced automatically by linters.

Examples

1. Our naming convention for branches is type/ticket-number-short-description.

2. These test files don't follow the naming convention, so the test runner skips them.

Common phrases

follow a naming convention · consistent naming convention · camelCase · snake_case

dead code

noun

Meaning

Code that is never run or whose result is never used, for example an old function nobody calls. It only makes the codebase harder to read.

Where you use it

Reviewers ask authors to remove dead code instead of commenting it out, since version control keeps the history anyway. Many IDEs and linters can detect unused functions and variables.

Examples

1. Half of this file is dead code from the old checkout, so let's delete it.

2. Don't comment out dead code; Git already remembers it.

Common phrases

remove dead code · clean up dead code · dead code elimination · unused code

DRY

abbreviation

Meaning

Short for 'Don't Repeat Yourself': the principle that each piece of knowledge or logic should exist in one place in the code instead of being copied around.

Where you use it

Pronounced like the word 'dry'. Reviewers write 'Let's DRY this up' or 'This isn't very DRY'. Applied too early, it can create the wrong abstraction, so some developers wait until code is repeated three times (the 'rule of three').

Examples

1. The same validation appears in four controllers; let's DRY it up with a shared helper.

2. Keeping code DRY is good, but don't merge two functions that only look similar by accident.

Common phrases

DRY principle · DRY it up · keep it DRY · not very DRY

unit test

noun

Meaning

A small automated test that checks one function or class on its own, separate from the database, the network and the rest of the system.

Where you use it

Teams write, run and fix unit tests, and reviewers often ask 'Can you add a unit test for this?' Unit tests should be fast enough to run on every commit in the CI pipeline.

Examples

1. Please add a unit test for the discount calculation before we merge.

2. All 450 unit tests pass in under ten seconds.

Common phrases

write a unit test · run the unit tests · add a unit test · unit tests pass

test case

noun

Meaning

One specific situation you check, with set inputs, steps and an expected result, for example 'logging in with a wrong password shows an error'.

Where you use it

Used by both developers and QA engineers. Manual testers write test cases in test management tools or spreadsheets; developers add test cases to automated test suites. Test cases pass, fail or are skipped.

Examples

1. Let's add a test case for an empty shopping cart.

2. QA wrote 30 test cases for the new payment flow.

Common phrases

write a test case · add a test case · failing test case · test case for

edge case

noun

Meaning

An unusual situation at the limits of what a program expects, such as an empty list, a very long name or a date like 29 February.

Where you use it

Very common in code reviews and planning: 'What about the edge case where the list is empty?' Developers handle, cover, miss and test edge cases.

Examples

1. Did you handle the edge case where the user has no orders yet?

2. Most of our production bugs come from edge cases we didn't test.

Common phrases

handle an edge case · cover edge cases · miss an edge case · test edge cases

QA

abbreviation

Meaning

Short for quality assurance: the work of checking that software meets its requirements and works well. It also names the people or team who do this work.

Where you use it

Used for the process, the team and the stage: 'send it to QA', 'QA found two bugs', 'It's in QA'. QA engineers do manual and automated testing, and a 'QA environment' is a server set aside for testing.

Examples

1. The ticket is done on our side and waiting for QA.

2. QA reported that the discount code still works after it expires.

Common phrases

send to QA · QA engineer · QA environment · pass QA · QA team

regression

noun

Meaning

A bug where something that used to work stops working after a change, such as a new feature breaking an old one.

Where you use it

QA teams run 'regression tests' before releases to catch these problems. People say 'This is a regression from version 4.1' or 'The refactor caused a regression in search.'

Examples

1. Search was fast last week, so this slowdown looks like a regression.

2. Full regression testing takes two days before each major release.

Usage note

In statistics and data science, 'regression' is a method for modeling relationships between variables; in testing it means something that got worse.

Common phrases

regression test · cause a regression · regression testing · performance regression

integration test

noun

Meaning

A test that checks how several parts of a system work together, for example your code with a real database or another service.

Where you use it

Sits between unit tests and end-to-end tests. Integration tests are slower than unit tests but catch problems in the connections between parts, such as wrong queries or changed API formats.

Examples

1. The unit tests passed, but the integration test failed against the real database.

2. We run integration tests in Docker so every developer gets the same setup.

Common phrases

write an integration test · run integration tests · integration test suite · integration testing

test coverage

noun

Meaning

A measure, often a percentage, of how much of the code is run by automated tests. It shows which parts are tested and which are not.

Where you use it

Teams measure, report and increase test coverage, and some CI pipelines fail if it drops below a set limit. Reviewers often point out that high coverage does not guarantee good tests.

Examples

1. Test coverage for the billing module is only 40 percent.

2. This PR adds tests for the error paths and raises test coverage to 85 percent.

Common phrases

increase test coverage · code coverage · coverage report · low test coverage

mock

noun

Meaning

A fake version of a real object or service used in tests, so you can control its behavior and check how your code uses it. Also a verb: to mock a service.

Where you use it

Developers create mocks for databases, payment providers and external APIs so that unit tests run fast and without a network. Common phrases: 'mock the API', 'mock out the clock', 'too many mocks'.

Examples

1. We mock the payment provider, so the tests never charge a real card.

2. This test has so many mocks that it doesn't test anything real.

Usage note

Testing experts separate 'mocks', 'stubs' and 'fakes', but in everyday talk many developers call all of them mocks.

Common phrases

mock a service · mock object · mock out · mock data

end-to-end test

noun

Meaning

A test that runs a complete user journey through the real system, for example opening the site, logging in and placing an order, to check that everything works together.

Where you use it

Usually shortened to 'E2E test'. Tools such as Playwright, Cypress and Selenium control a real browser. E2E tests give high confidence but are slow and can be flaky, so teams keep only the most important ones.

Examples

1. Our end-to-end tests cover sign-up, checkout and password reset.

2. The end-to-end test failed because the email service on staging was down.

Common phrases

write end-to-end tests · E2E test suite · run end-to-end tests · end-to-end testing

flaky

adjective

Meaning

Describing a test that sometimes passes and sometimes fails without any change to the code, often because of timing, the network or shared data.

Where you use it

Mostly said about tests and CI: 'a flaky test', 'This test is flaky, just rerun it.' Teams track, quarantine and fix flaky tests because they slowly destroy trust in CI. In everyday English, 'flaky' also describes unreliable people.

Examples

1. The payment test is flaky. It fails about once in every ten runs.

2. Don't just rerun the pipeline; please open a ticket for the flaky test.

Common phrases

flaky test · flaky build · quarantine flaky tests · fix a flaky test

test suite

noun

Meaning

A collection of tests that are run together, for example all the unit tests of a project or every test for the payment module.

Where you use it

People run, extend or speed up the test suite. 'The full suite takes 20 minutes' is a common complaint. CI pipelines run the test suite on every pull request, and a green suite means that all tests passed.

Examples

1. The whole test suite passes locally, but two tests fail on CI.

2. Let's split the test suite so the slow integration tests run only at night.

Common phrases

run the test suite · full test suite · the test suite passes · speed up the test suite

manual testing

noun

Meaning

Checking software by hand, with a person clicking through screens and trying actions, instead of using test scripts that run automatically.

Where you use it

Still useful for new features, user experience and exploratory testing, but slow and hard to repeat. Teams try to reduce manual testing before each release by adding automated tests. You 'do manual testing' or 'test something manually'.

Examples

1. Manual testing of the checkout flow takes the QA team half a day before every release.

2. We can't rely on manual testing forever, so let's automate the login scenarios first.

Common phrases

do manual testing · manual testing effort · reduce manual testing · exploratory testing

automated testing

noun

Meaning

Using code and tools to run tests automatically and compare the results with what is expected, so they can be repeated quickly after every change.

Where you use it

Covers the unit, integration and end-to-end tests that run in CI. People say 'invest in automated testing', 'the automated tests caught it' and 'test automation engineer'. It makes refactoring and frequent releases safer.

Examples

1. Without automated testing, every small change needed a full day of manual checks.

2. We started automated testing with the API layer because it changes the least.

Common phrases

invest in automated testing · test automation · automated test suite · automated testing framework

assertion

noun

Meaning

A line in a test that checks whether a result matches the expected value. If the check is false, the test fails.

Where you use it

Written with functions such as assertEquals, expect(...).toBe(...) or Python's assert. Reviewers ask for 'a stronger assertion' when a test checks too little. 'Assertion failed' or 'AssertionError' in the output tells you which check broke.

Examples

1. This test has no assertions, so it passes even when the function returns garbage.

2. Add an assertion for the error message, not just for the status code.

Common phrases

add an assertion · the assertion fails · assertion error · a stronger assertion

smoke test

noun

Meaning

A quick, basic test that checks the most important functions work at all, for example that the app starts and users can log in, before deeper testing.

Where you use it

Often run right after a deploy: 'Run a smoke test on staging.' If the smoke test fails, there is no point running the full test suite. The name comes from hardware testing: switch the device on and see whether smoke comes out.

Examples

1. After each deploy, the pipeline runs a smoke test against the login and search pages.

2. The smoke test failed on staging, so we stopped the release.

Common phrases

run a smoke test · the smoke test fails · post-deploy smoke test · smoke testing

happy path

noun

Meaning

The normal scenario in which everything goes as expected: the user enters valid data, nothing fails and the task completes successfully.

Where you use it

Used in testing and design discussions: 'We've only tested the happy path.' The opposites are edge cases, error paths or the 'unhappy path'. Good tests cover both.

Examples

1. The demo covers the happy path, but what happens if the card is declined?

2. We only tested the happy path, which is why the empty-cart bug reached production.

Common phrases

test the happy path · happy path scenario · beyond the happy path · unhappy path

TDD

abbreviation

Meaning

Short for test-driven development: writing a failing test first, then the code that makes it pass, then cleaning up the code, in short repeated cycles.

Where you use it

The cycle is often called 'red, green, refactor'. Said letter by letter: T-D-D. People 'do TDD', 'practice TDD' or 'write it test-first'. Teams disagree on how strictly to follow it, but the vocabulary comes up often in interviews.

Examples

1. We used TDD for the pricing rules because the edge cases were so tricky.

2. With TDD, I write a test for the bug first and watch it fail.

Common phrases

practice TDD · red, green, refactor · test-first · TDD cycle

test environment

noun

Meaning

A separate copy of a system, with its own servers, data and settings, where software is tested without affecting real users.

Where you use it

Teams usually have several environments, such as development, test or QA, staging and production. 'It works in the test environment but not in production' often points to different configuration or data. Testers ask for test data and access to the test environment.

Examples

1. The test environment uses a copy of last month's data with personal details removed.

2. Deploy your branch to the test environment so QA can check it.

Common phrases

deploy to the test environment · set up a test environment · test data · shared test environment

UAT

abbreviation

Meaning

Short for user acceptance testing: the last testing stage, in which real users or the client check that the software meets their needs before it goes live.

Where you use it

Said letter by letter (U-A-T). It can mean the phase ('we're in UAT') or the environment ('deploy it to UAT'). Common in agency, banking and enterprise projects, where the client must sign off before the release.

Examples

1. The new reports are in UAT this week, and the finance team is testing them.

2. The client found two issues during UAT, so the go-live moves to next month.

Common phrases

UAT environment · UAT sign-off · in UAT · UAT phase

crash report

noun

Meaning

A record created when an app crashes, showing the error, the stack trace, the device, the OS version and other details that help developers find the cause.

Where you use it

Developers read, symbolicate and group crash reports in tools such as Firebase Crashlytics, Sentry, Xcode Organizer and Google Play vitals. To make the reports readable, iOS teams upload dSYM files and Android teams upload R8 or ProGuard mapping files.

Examples

1. The crash report shows a null value on the checkout screen.

2. We get hundreds of crash reports from just one device model.

Common phrases

read a crash report · crash reporting tool · symbolicate a crash report · send crash reports

analytics

noun

Meaning

Data about how people use an app, such as which screens they open and where they leave, collected as events to understand behavior and measure features.

Where you use it

Teams add analytics events, check analytics dashboards and talk about daily active users (DAU), retention and funnels. Common tools include Firebase Analytics, Amplitude and Mixpanel. Collecting analytics may require user consent and must be declared in the stores' privacy forms.

Examples

1. According to our analytics, most users never open the settings screen.

2. Add an analytics event when the user taps Buy.

Common phrases

analytics event · analytics dashboard · track in analytics · analytics SDK

crash-free rate

noun

Meaning

The percentage of users or sessions that did not experience a crash in a given period; a key measure of an app's stability.

Where you use it

Crash reporting tools show crash-free users and crash-free sessions. Mature apps often aim for 99.5% or higher, and teams compare the rate between releases when deciding whether to continue a staged rollout.

Examples

1. Our crash-free rate dropped to 98.7% after the last update.

2. We won't go beyond 20% rollout until the crash-free rate is back above 99.5%.

Usage note

English uses a decimal point (99.5%), while Turkish uses a comma (%99,5) and puts the percent sign first.

Common phrases

crash-free users · crash-free sessions · crash-free rate · app stability

device fragmentation

noun

Meaning

The wide variety of devices, screen sizes, hardware and operating system versions an app must work on, which makes testing harder, especially on Android.

Where you use it

Android developers often mention fragmentation to explain why a bug appears only on one manufacturer's phones. Teams handle it with device labs, cloud testing services such as Firebase Test Lab, and analytics that show which devices their users actually have.

Examples

1. Device fragmentation means we can't test on every phone, so we focus on the top 20 models.

2. Device fragmentation is the main reason our Android QA takes longer than iOS.

Common phrases

device fragmentation · Android fragmentation · OS fragmentation · deal with fragmentation

UI test

noun

Meaning

An automated test that uses the app the way a person would, tapping buttons, typing text and checking what appears on the screen.

Where you use it

iOS teams write UI tests with XCUITest, and Android teams use Espresso or Compose testing tools; cross-platform options include Appium and Maestro. UI tests are slower and break more easily than unit tests, so teams usually keep them for the most important flows.

Examples

1. The UI test for sign-up fails randomly on CI; I think it's a timing problem.

2. We have UI tests for login, search and checkout.

Common phrases

write a UI test · UI test fails · flaky UI test · run UI tests on CI

battery drain

noun

Meaning

Faster than normal battery use caused by an app, for example through constant location tracking, frequent network calls or work that keeps running in the background.

Where you use it

Users complain about battery drain in store reviews, and both platforms show which apps use the most battery. Android's Doze mode and the background limits on iOS exist largely to reduce it. Developers check energy use with Xcode's tools and the Android Studio profiler.

Examples

1. Several reviews mention battery drain since we added live location sharing.

2. The battery drain comes from a timer that keeps running after the user leaves the screen.

Common phrases

battery drain · drain the battery · battery usage · energy impact

app size

noun

Meaning

How much space an app needs, both as a download from the store and after installation on the device, including its code, images and libraries.

Where you use it

Teams track download size and install size, and reduce app size by removing unused libraries, compressing images and using platform features such as app thinning on iOS and Android App Bundles, which deliver only the parts each device needs.

Examples

1. The app size went from 60 MB to 95 MB after we added the video SDK.

2. Reducing app size matters in markets where many users have little free storage.

Common phrases

reduce app size · download size · install size · app size budget

ANR

abbreviation

Meaning

Application Not Responding: an Android error shown when an app's main thread is blocked for too long, for example about five seconds without responding to a touch.

Where you use it

Users see a dialog that lets them wait or close the app. Teams follow the ANR rate in Google Play vitals, because a high rate can reduce an app's visibility in the store. The usual fix is to move slow work off the main thread.

Examples

1. We get ANRs on cheap phones when the app parses a big JSON file at startup.

2. Our ANR rate in Play vitals is above the bad behavior threshold.

Usage note

iOS has no ANR dialog; iOS developers talk about 'hangs', which Xcode Organizer reports separately.

Common phrases

ANR rate · get an ANR · ANR dialog · Android vitals

prototype

noun

Meaning

A quick, rough version of a game or feature made to test whether an idea is fun or works, before the team spends time on final art and polish.

Where you use it

Prototypes are often ugly on purpose, with grey boxes and placeholder sounds. You build, test, throw away or greenlight a prototype. It is also a verb: to prototype a mechanic. A paper prototype uses cards or drawings instead of code.

Examples

1. We built a prototype in two weeks just to see if the grappling hook was fun.

2. Don't polish the prototype; we might throw the whole idea away.

Common phrases

build a prototype · rapid prototype · paper prototype · playable prototype · prototype a mechanic

playtest

noun

Meaning

A session in which people play an unfinished version of the game while the team watches and collects feedback on fun, difficulty and confusing moments.

Where you use it

Also a verb: we playtested the new level. Internal playtests use team members; external playtests bring in players who have never seen the game. The players are called playtesters. A key rule is to watch quietly and not explain the game.

Examples

1. In yesterday's playtest, four of six players missed the hidden door.

2. Let's playtest the boss fight with people outside the team.

Usage note

A playtest is about the player experience: is it fun and clear? QA testing is about finding bugs. Studios do both, but they are different jobs.

Common phrases

run a playtest · external playtest · playtest session · playtest feedback · playtester

milestone

noun

Meaning

An agreed point in development when specific work must be delivered and reviewed, such as a playable demo, alpha or beta; publishers often pay the studio per milestone.

Where you use it

Producers plan milestones and their deliverables. Teams hit, miss, deliver or slip milestones. In publishing contracts, milestone payments keep independent studios running, so a missed milestone can be serious.

Examples

1. The next milestone is a 15-minute playable demo for the publisher.

2. If we miss this milestone, the payment is delayed by a month.

Common phrases

hit a milestone · milestone payment · milestone build · miss a milestone · milestone review

alpha

noun

Meaning

The stage of development when all main features are in the game and it can be played from start to finish, but it still has many bugs, placeholders and no polish.

Where you use it

Definitions differ between studios, so check what your publisher means by alpha. People talk about reaching alpha, an alpha build and a closed alpha test with selected players. After alpha comes beta.

Examples

1. We hit alpha last week: every level is in, but half of them still use grey boxes.

2. The closed alpha is only for 500 players who signed an NDA.

Common phrases

reach alpha · alpha build · closed alpha · alpha milestone · feature complete

beta

noun

Meaning

The stage after alpha when the game's content is complete and the team focuses on fixing bugs and polishing; also a public or closed test of that version.

Where you use it

Usually no new features are added after beta. Open betas let anyone play, test the servers and build interest before launch. American English says BAY-ta; British English often says BEE-ta.

Examples

1. We're in beta now, so no more new features, only bug fixes.

2. The open beta crashed our login servers on the first night.

Common phrases

open beta · closed beta · beta test · beta build · beta key

vertical slice

noun

Meaning

A short but fully finished part of a game, such as one level, that shows final quality in art, sound and gameplay to prove what the whole game will be like.

Where you use it

Studios build a vertical slice to convince publishers or investors, or to test their production pipeline. It is different from a prototype, which is rough and tests only the idea. You build, deliver and demo a vertical slice.

Examples

1. The publisher wants to see a vertical slice before they commit to full funding.

2. Our vertical slice is the harbor level with final art, music and two enemy types.

Usage note

Think of a cake cut from top to bottom: one thin slice shows every layer.

Common phrases

build a vertical slice · vertical slice demo · deliver a vertical slice · vertical slice milestone

usability

noun

Meaning

How easily, quickly and successfully people can use a product to complete a task, and how satisfied they feel while doing it.

Where you use it

Used in design reviews, test reports and job ads: usability issues, usability problems, good usability. The ISO 9241-11 standard describes it through three qualities: effectiveness, efficiency and satisfaction.

Examples

1. The design looks great, but we found serious usability problems in the payment step.

2. Small changes to labels can improve usability a lot.

Usage note

Usability is not the same as accessibility: a product can be easy for most people and still be impossible to use with a screen reader.

Common phrases

usability issue · improve usability · usability problem · usability expert

usability testing

noun

Meaning

A research method in which real users try to complete tasks with a product or prototype while a researcher watches, to find out where they struggle.

Where you use it

Teams run usability tests in person or remotely, moderated or unmoderated, and turn the results into a list of issues ranked by severity. A well-known rule of thumb from Jakob Nielsen says that about five users reveal most of the major problems.

Examples

1. We're running usability testing on the new sign-up flow next Tuesday.

2. Usability testing showed that four out of five people missed the filter button.

Common phrases

run usability testing · remote usability testing · usability testing session · usability test script

heuristic evaluation

noun

Meaning

A review in which usability experts check an interface against a list of accepted design principles, called heuristics, to find problems without testing with users.

Where you use it

The best-known list is Jakob Nielsen's ten usability heuristics, such as 'visibility of system status' and 'error prevention'. It is quick and cheap, but it complements usability testing rather than replacing it.

Examples

1. A quick heuristic evaluation found fifteen issues before we even recruited users.

2. Two designers did a heuristic evaluation of the admin panel separately and then compared notes.

Usage note

Heuristic is pronounced hyoo-RIS-tik. A heuristic is a rule of thumb, not a strict law.

Common phrases

conduct a heuristic evaluation · usability heuristics · heuristic review · Nielsen's heuristics

think-aloud protocol

noun

Meaning

A testing technique in which participants say what they are thinking, looking for and feeling while they use a product, so researchers can follow their reasoning.

Where you use it

The standard technique in moderated usability tests. The moderator asks participants to think aloud and gently reminds them ('What are you thinking now?') when they go quiet. People also say 'think-aloud session' or 'think-aloud test'.

Examples

1. We used the think-aloud protocol, so every session recording includes the participant's comments.

2. The think-aloud protocol revealed that users read 'Archive' as 'Delete'.

Common phrases

use the think-aloud protocol · think-aloud session · ask participants to think aloud · concurrent think-aloud

task success rate

noun

Meaning

The percentage of participants who complete a given task correctly in a usability test; one of the simplest and most common usability metrics.

Where you use it

Often reported together with time on task, error rate and satisfaction scores. Teams compare task success rates before and after a redesign. Also called task completion rate.

Examples

1. The task success rate for changing a delivery address rose from 40% to 90%.

2. A low task success rate on this step tells us the label is confusing.

Common phrases

measure task success rate · high task success rate · time on task · usability metrics

moderated testing

noun

Meaning

Usability testing in which a researcher guides each session live, in person or on a video call, giving tasks, asking questions and observing the participant.

Where you use it

The opposite is unmoderated testing, where participants complete tasks alone in an online tool while their screens are recorded. Moderated tests give richer insights; unmoderated tests are faster and cheaper at scale.

Examples

1. We chose moderated testing because the flow is complex and we want to ask follow-up questions.

2. Unmoderated testing gave us 50 recordings in two days.

Common phrases

moderated usability testing · unmoderated testing · remote moderated session · moderator guide

bug

noun

Meaning

A mistake in a program that makes it behave in a way nobody intended, such as showing wrong results, freezing or closing suddenly.

Where you use it

The most common word for a software problem in daily work. You find, report, track down and fix bugs. In formal reports and some tracking tools you will also see 'defect' or 'issue'.

Examples

1. QA found a bug on the checkout page: the total doesn't update when you remove an item.

2. This bug only shows up when two users edit the same record at the same time.

3. Before we add new features, let's fix the critical bugs from last week.

Common phrases

fix a bug · report a bug · track down a bug · critical bug · bug report

fix

verb

Meaning

To change code so that a problem no longer happens. As a noun, 'a fix' is the change that solves the problem.

Where you use it

Used constantly in stand-ups, commit messages and tickets: 'I fixed the login issue', 'Fix typo in README'. The noun is just as common: 'push a fix', 'a quick fix', 'the fix is in review'.

Examples

1. I fixed the timeout issue yesterday, but it still needs a review.

2. The fix is small: we were comparing dates in two different time zones.

Usage note

Many teams write commit messages in the imperative: 'Fix crash on empty list', not 'Fixed crash' or 'Fixing crash'.

Common phrases

fix a bug · fix an issue · a quick fix · push a fix · bug fix

debug

verb

Meaning

To search for the cause of a problem in a program and remove it, often by running the code step by step and checking values.

Where you use it

Developers debug code, a crash or a failing test. You debug locally, attach a debugger or, carefully, debug in production. The -ing form is very common: 'I spent the morning debugging.'

Examples

1. I spent two hours debugging a test that only failed on Mondays.

2. Can you help me debug this? The API returns an empty list.

Common phrases

debug an issue · debug locally · debug a crash · debugging session · use a debugger

crash

verb

Meaning

To stop working suddenly because of an error, so that the program closes or stops responding. Also a noun: 'a crash'.

Where you use it

Apps, servers and browsers crash. Teams look at 'crash reports', 'crash logs' and the 'crash rate'. It is also used with an object: 'This input crashes the parser.'

Examples

1. The app crashes when you rotate the phone on the settings screen.

2. After the update, the crash rate on Android dropped by half.

Common phrases

the app crashes · crash report · crash on startup · crash rate · cause a crash

reproduce

verb

Meaning

To make a bug happen again on purpose by following the same steps, so that you can see it yourself and find its cause.

Where you use it

One of the first questions about any bug: 'Can you reproduce it?' Developers often shorten it to 'repro'. Bug reports include 'steps to reproduce', and a bug can be easy, hard or impossible to reproduce.

Examples

1. I can't reproduce the issue on my machine. Which browser are you using?

2. Please add clear steps to reproduce to the bug report.

Usage note

In everyday English 'reproduce' also means to have young or to copy something, but in software it almost always means making a bug happen again.

Common phrases

reproduce a bug · steps to reproduce · can't reproduce · hard to reproduce

log

noun

Meaning

A record of events, messages and errors that a program writes while it runs, used later to understand what happened. Also a verb: to log an error.

Where you use it

Usually plural: 'check the logs', 'the server logs'. As a verb you log an error or a warning. Log levels such as DEBUG, INFO, WARN and ERROR control how much detail is written.

Examples

1. Check the logs around 14:05; that's when the payments started failing.

2. We log every failed login attempt, but never the password.

Common phrases

check the logs · error log · log an error · log level · server logs

stack trace

noun

Meaning

A report printed when an error happens, listing the chain of function calls that led to it, with file names and line numbers.

Where you use it

Developers paste stack traces into tickets and chat: 'Here's the full stack trace.' When reading one, you look for the first line that points to your own code rather than to a library.

Examples

1. Can you paste the full stack trace? The last line alone doesn't help.

2. The stack trace points to line 88 in OrderService.

Usage note

Python calls it a 'traceback', and it shows the most recent call last, at the bottom.

Common phrases

full stack trace · read a stack trace · paste the stack trace · the stack trace points to

root cause

noun

Meaning

The deepest, original reason a problem happened, as opposed to the symptoms that people noticed first.

Where you use it

Common in incident reviews and bug tickets: 'find the root cause', 'root cause analysis (RCA)'. A quick fix may hide the symptom, but the team still needs to deal with the root cause.

Examples

1. Restarting the server helped, but we still don't know the root cause.

2. The root cause was an expired certificate on the payment gateway.

Common phrases

find the root cause · root cause analysis · identify the root cause · fix the root cause

workaround

noun

Meaning

A temporary way to avoid a problem without really fixing it, so that work can continue until a proper solution is ready.

Where you use it

Used in bug reports, support and team chat: 'Is there a workaround?', 'As a workaround, clear the cache.' Teams try not to leave workarounds in place for too long, because they turn into technical debt.

Examples

1. Until the library is fixed, the workaround is to pin version 2.3.

2. Support told the customer about a workaround while we prepared a hotfix.

Usage note

The noun is one word, 'workaround'; the phrasal verb is two words: 'We can work around the problem.'

Common phrases

temporary workaround · find a workaround · as a workaround · use a workaround

exception

noun

Meaning

An error event that interrupts the normal flow of a program. The code can catch and handle it, or it can make the program crash.

Where you use it

In Java, C# and JavaScript code 'throws' exceptions; in Python it 'raises' them. You catch, handle, log and sometimes wrongly swallow exceptions. 'Unhandled exception' and 'null pointer exception' are classic phrases.

Examples

1. The parser throws an exception if the date format is wrong.

2. Don't just catch the exception and ignore it. At least log it.

Common phrases

throw an exception · catch an exception · handle an exception · unhandled exception · null pointer exception

breakpoint

noun

Meaning

A marker you put on a line of code so that the program pauses there while it runs, letting you inspect variables and step through the code.

Where you use it

You set, hit and remove breakpoints in an IDE or in the browser's developer tools. A 'conditional breakpoint' stops only when a condition is true. Many developers still use print statements instead.

Examples

1. Set a breakpoint inside the loop and check what the total is on each pass.

2. The breakpoint never gets hit, so this code path isn't running at all.

Usage note

In web design, a breakpoint is something else: the screen width at which a responsive layout changes.

Common phrases

set a breakpoint · hit a breakpoint · conditional breakpoint · remove all breakpoints

error message

noun

Meaning

Text that a program shows when something goes wrong, saying what failed and sometimes why, for example 'File not found' or 'Connection refused'.

Where you use it

The first thing to read when debugging and the first thing to share when asking for help: 'What's the exact error message?' Developers often paste error messages into a search engine. Good error messages also tell users what to do next.

Examples

1. Can you send me the full error message instead of a screenshot?

2. The error message says the port is already in use.

Common phrases

get an error message · the exact error message · clear error message · user-friendly error message

troubleshoot

verb

Meaning

To look for the cause of a problem step by step and fix it, especially in a running system, a setup or a user's environment.

Where you use it

Close to 'debug' but wider: you debug code, while you can troubleshoot anything, such as network problems, failed installs or a slow server. Documentation often has a 'Troubleshooting' section that lists common problems and fixes.

Examples

1. I spent the morning troubleshooting why the build agent couldn't reach the registry.

2. Before you open a ticket, check the troubleshooting section of the README.

Common phrases

troubleshoot an issue · troubleshooting guide · troubleshooting steps · help troubleshoot

bug report

noun

Meaning

A written description of a problem in software, usually saying what happened, what should have happened and how to make it happen again.

Where you use it

Filed by testers, users or developers in a tracker such as Jira or GitHub Issues. A good bug report includes steps to reproduce, expected and actual behavior, environment details, and screenshots or logs. You file, triage or close a bug report.

Examples

1. Thanks for the detailed bug report; I could reproduce the issue in two minutes.

2. We got three bug reports about the checkout page after the release.

Common phrases

file a bug report · detailed bug report · bug report template · triage bug reports

syntax error

noun

Meaning

A mistake in how code is written, such as a missing bracket or a misspelled keyword, which stops the program from compiling or running.

Where you use it

Usually easy to fix because the compiler, interpreter or IDE points to the exact line. Compare it with a logic error, where the code runs but gives the wrong result. Linters catch many syntax errors before you even run the code.

Examples

1. The deploy failed because of a syntax error in the YAML file: a missing colon.

2. Your IDE underlines syntax errors in red as you type.

Common phrases

fix a syntax error · get a syntax error · syntax error on line · unexpected token

debugger

noun

Meaning

A tool that lets you pause a running program, go through it line by line and look at the values of variables to find out why it misbehaves.

Where you use it

Most IDEs have a built-in debugger. You attach a debugger to a process, run the code in the debugger and set breakpoints. Many developers start with print statements but switch to a debugger for harder bugs.

Examples

1. Run it in the debugger and check what the variable holds before the crash.

2. I attached the debugger to the running container and found the bad config value.

Common phrases

attach a debugger · run in the debugger · built-in debugger · debugger session

step through

phrasal verb

Meaning

To run code one line or instruction at a time in a debugger, checking what happens after each step.

Where you use it

Used with debuggers and breakpoints: 'step through the function', 'step through it line by line'. Related commands are 'step over' (run a function call as one step), 'step into' (go inside it) and 'step out'. In meetings, the similar 'walk through' means explaining something step by step.

Examples

1. I stepped through the loop and saw that the counter was never reset.

2. Set a breakpoint here and step through the parser with the failing input.

Common phrases

step through the code · step through line by line · step over · step into

error handling

noun

Meaning

Code that deals with things going wrong, such as a failed request or bad input, so the program can recover, retry or show a clear message instead of crashing.

Where you use it

Usually written with try/catch (or try/except) blocks: one piece of code 'throws' an exception and another 'catches' it. Reviewers comment on 'missing error handling' or ask you to 'handle the error'. Silently swallowing errors is a well-known bad habit.

Examples

1. There's no error handling here: if the payment API is down, the whole page crashes.

2. Let's add error handling around the file upload and show the user a friendly message.

Common phrases

add error handling · proper error handling · try/catch block · swallow an error

memory leak

noun

Meaning

A bug where a program keeps memory it no longer needs, so its memory use grows over time until it slows down or crashes.

Where you use it

Typical signs are memory usage that only goes up and a service that has to be restarted every few days. Common causes include event listeners or caches that are never cleared. Developers track down and fix a memory leak with a profiler.

Examples

1. The worker uses 4 GB after a week, so we probably have a memory leak.

2. The memory leak came from a cache that never removed old entries.

Common phrases

track down a memory leak · fix a memory leak · memory usage · memory profiler

infinite loop

noun

Meaning

A loop that never stops because its exit condition is never met, which can freeze a program or use 100% of the CPU.

Where you use it

Usually a bug, for example when a counter is never increased. People say 'it's stuck in an infinite loop' or 'it goes into an infinite loop'. Sometimes it is intentional, as in a server's main loop written with while (true).

Examples

1. The page froze because the retry logic got stuck in an infinite loop.

2. If the API keeps returning the same cursor, this code will turn into an infinite loop.

Common phrases

stuck in an infinite loop · cause an infinite loop · go into an infinite loop · break out of the loop

off-by-one error

noun

Meaning

A common bug where a loop or calculation goes one step too far or stops one step too early, often because counting starts at zero.

Where you use it

Typical causes are using <= instead of <, or forgetting that the last index is the length minus one. A well-known joke says there are two hard problems in computer science: naming things, cache invalidation and off-by-one errors.

Examples

1. The report missed the last day of the month because of an off-by-one error in the date range.

2. Check the loop condition; it looks like a classic off-by-one error.

Common phrases

classic off-by-one error · off-by-one bug · fix an off-by-one error · fencepost error

steps to reproduce

phrase

Meaning

The exact list of actions someone must take to make a bug appear again, written in a bug report so a developer can see the problem for themselves.

Where you use it

A standard section of bug report templates, usually next to 'Expected result' and 'Actual result', and written as a numbered list. Developers ask 'Do you have steps to reproduce?' or use the short forms STR and 'repro steps'.

Examples

1. The ticket has no steps to reproduce, so I asked the customer for more details.

2. Steps to reproduce: 1. Log in. 2. Open Settings. 3. Change the language to Turkish.

Common phrases

add steps to reproduce · clear steps to reproduce · repro steps · expected vs actual result

monitoring

noun

Meaning

Continuously collecting and checking data about systems, such as CPU use, error rates and response times, so that problems are noticed quickly.

Where you use it

Used as an uncountable noun: 'we need better monitoring', 'monitoring tools', 'add monitoring for the queue'. Common tools are Prometheus, Grafana, Datadog and Amazon CloudWatch. The verb is 'monitor'.

Examples

1. Our monitoring showed the disk filling up two days before it became a problem.

2. Before the launch, make sure monitoring is in place for the new service.

Common phrases

monitoring tool · set up monitoring · monitoring system · uptime monitoring · infrastructure monitoring

alert

noun

Meaning

An automatic notification sent to engineers when a monitored value crosses a limit or something looks wrong, for example when the error rate is too high.

Where you use it

Alerts fire, trigger, go off and get resolved or acknowledged. Too many unimportant ones cause 'alert fatigue', and engineers learn to ignore them. Alerts often go to Slack, email or paging tools like PagerDuty.

Examples

1. An alert fired at 2 a.m. because the queue had more than 10,000 messages waiting.

2. This alert is too noisy. Let's raise the threshold so it only fires for real problems.

Common phrases

an alert fires · alert threshold · acknowledge an alert · alert fatigue · noisy alert

incident

noun

Meaning

An unplanned event that disrupts a service or makes it worse for users, such as an outage, a big slowdown or a data problem, and that needs a quick response.

Where you use it

Incidents are declared, handled, escalated and resolved. Many companies rate them by severity, such as SEV1 for the most serious. An incident commander coordinates the response, and a postmortem follows.

Examples

1. We declared an incident when checkout errors jumped to 30 percent.

2. The incident lasted forty minutes and was caused by an expired certificate.

Usage note

In everyday English an incident can be any event, even a small accident. In operations it means a service problem, not a traffic accident.

Common phrases

declare an incident · incident response · major incident · incident commander · resolve an incident

outage

noun

Meaning

A period when a service, system or part of it is not working or cannot be reached by users.

Where you use it

Outages can be full or partial, planned or unplanned. You experience, cause, report and recover from an outage. Big provider outages often make the news and appear on public status pages.

Examples

1. A partial outage in the storage service made image uploads fail for an hour.

2. The outage started right after the config change, so we rolled it back.

Usage note

In British English 'power cut' is common for electricity; 'power outage' is more American. In IT, 'outage' is standard everywhere.

Common phrases

partial outage · major outage · cause an outage · outage window · unplanned outage

downtime

noun

Meaning

The amount of time a system or service is not available to users, either because of a failure or because of planned maintenance.

Where you use it

Uncountable: 'two hours of downtime', 'minimize downtime'. 'Planned downtime' is announced maintenance; 'zero-downtime deployment' means releasing without interrupting users. The opposite is uptime.

Examples

1. The database upgrade needs about fifteen minutes of downtime, so we'll do it at night.

2. Every hour of downtime costs the shop thousands of euros in lost orders.

Common phrases

planned downtime · minimize downtime · zero-downtime deployment · unexpected downtime

uptime

noun

Meaning

The time or percentage of time that a system is working and available, often written as a figure such as 99.9 percent over a month or a year.

Where you use it

Engineers talk in 'nines': 'three nines' is 99.9 percent (about 8.8 hours of downtime a year), 'four nines' is 99.99 percent (about 53 minutes a year). Uptime figures appear in SLAs and on status pages.

Examples

1. We had 99.95 percent uptime last quarter, just above our target.

2. An uptime monitor checks the homepage every minute from five countries.

Common phrases

99.9 percent uptime · uptime monitoring · guarantee uptime · improve uptime

SLA

abbreviation

Meaning

Short for service level agreement: a contract that promises customers a certain level of service, such as 99.9 percent uptime, and says what happens if it is not met.

Where you use it

Said letter by letter, 'S-L-A'. Cloud providers often give service credits (a discount on the bill) when they break an SLA. Teams say a provider 'meets' or 'breaches' its SLA.

Examples

1. The SLA promises 99.9 percent availability, so this outage means we get a service credit.

2. Our enterprise customers ask for a four-hour response time in the SLA.

Usage note

SLA is a promise to customers with consequences; an SLO is an internal target, usually set stricter than the SLA.

Common phrases

meet the SLA · breach the SLA · SLA credit · uptime SLA

on-call

adjective

Meaning

Available outside normal hours to respond quickly if an alert or incident happens. Engineers take turns being on call for their services.

Where you use it

Written with a hyphen before a noun ('on-call engineer', 'on-call rotation') and without one after a verb ('I'm on call this week'). The on-call person 'gets paged' when an alert fires.

Examples

1. I'm on call this weekend, so I'll keep my laptop with me.

2. The on-call engineer got paged twice last night for the same disk alert.

Common phrases

on-call engineer · on-call rotation · be on call · on-call shift · on-call handover

metric

noun

Meaning

A number measured regularly over time to show how a system is behaving, such as CPU use, memory, request count or error rate.

Where you use it

Metrics are collected, exported, scraped, stored and shown on dashboards. Prometheus and CloudWatch are common tools. Alerts are usually based on metrics crossing a threshold.

Examples

1. The memory metric has been climbing for a week, which looks like a memory leak.

2. Let's add a metric for queue length so we can alert on it.

Usage note

Do not confuse 'metric' (a measurement) with 'the metric system' (metres and kilograms).

Common phrases

collect metrics · key metrics · custom metric · error rate metric · metrics dashboard

dashboard

noun

Meaning

A screen that shows the most important metrics and charts about a system in one place, so engineers can see its health at a glance.

Where you use it

Engineers build, share and check dashboards, often in Grafana, Datadog or CloudWatch. During an incident people say 'look at the dashboard' or 'the dashboard is all red'.

Examples

1. I've added the new payment service to the main dashboard.

2. The dashboard shows a clear drop in traffic at 14:05, right after the deploy.

Common phrases

Grafana dashboard · build a dashboard · monitoring dashboard · on the dashboard

observability

noun

Meaning

How well you can understand what is happening inside a system from the data it produces, especially logs, metrics and traces, even for problems nobody predicted.

Where you use it

Logs, metrics and traces are often called the 'three pillars of observability'. OpenTelemetry is a common open standard for collecting this data. The short form 'o11y' appears in chats and tool names.

Examples

1. Monitoring told us the API was slow; good observability showed us exactly which query was the cause.

2. We're investing in observability before we split the monolith into microservices.

Usage note

Monitoring checks for problems you already know about; observability helps you investigate problems you did not expect.

Common phrases

observability platform · improve observability · three pillars of observability · observability tools

tracing

noun

Meaning

Following a single request as it passes through many services, recording how long each step takes, so you can see where time is lost or errors happen.

Where you use it

Usually 'distributed tracing'. One request produces a trace, made of spans (one per step), linked by a trace ID. Tools include Jaeger, Zipkin and OpenTelemetry. Very useful with microservices.

Examples

1. Distributed tracing showed that 80 percent of the response time was spent waiting for the stock service.

2. Add the trace ID to every log line so tracing and logs can be linked.

Common phrases

distributed tracing · trace ID · tracing data · enable tracing

health check

noun

Meaning

A regular automatic test, often a request to a special URL such as /health, that checks whether a server or service is working and able to take traffic.

Where you use it

Load balancers use health checks to stop sending traffic to broken servers. Kubernetes has liveness probes (restart if stuck) and readiness probes (send traffic only when ready). Health checks pass or fail.

Examples

1. The health check failed three times, so the load balancer stopped sending traffic to that instance.

2. Our health check endpoint also tests the database connection, not just the web server.

Common phrases

health check endpoint · failed health check · readiness probe · liveness probe

postmortem

noun

Meaning

A written review after an incident that explains what happened, the impact, the timeline, the root cause and the actions that will stop it happening again.

Where you use it

Good teams write 'blameless postmortems' that focus on systems and processes, not on who made a mistake. Also called a post-incident review or incident report. Ends with action items that have owners.

Examples

1. The postmortem found that the alert existed but went to a channel nobody watched.

2. Please write the postmortem by Friday and add an owner to each action item.

Usage note

In medicine a post-mortem is an examination of a dead body (otopsi). In DevOps it only means an incident review.

Common phrases

blameless postmortem · write a postmortem · postmortem review · action items

redundancy

noun

Meaning

Having extra copies of servers, network links, disks or data, so that the system keeps working if one of them fails.

Where you use it

Engineers 'build in' or 'add' redundancy. 'N+1' means one more unit than you need. The adjective is 'redundant': 'redundant power supplies'. The goal is to avoid a single point of failure.

Examples

1. We added redundancy by running two NAT gateways instead of one.

2. The network has redundant links, so cutting one cable didn't cause an outage.

Usage note

In British English 'redundancy' also means losing your job because the position is no longer needed. In IT it means extra backup capacity.

Common phrases

build in redundancy · redundant system · single point of failure · N+1 redundancy

disaster recovery

noun

Meaning

The plans, tools and processes for bringing systems and data back after a major event, such as losing a whole data center or region.

Where you use it

Shortened to DR. Two key targets are RTO (recovery time objective: how quickly you must be back) and RPO (recovery point objective: how much recent data you can afford to lose). Teams run DR drills to test the plan.

Examples

1. Our disaster recovery plan says we must be back online in another region within four hours.

2. During the disaster recovery drill, we found that two services had no backups at all.

Common phrases

disaster recovery plan · DR site · disaster recovery drill · RTO and RPO

SLO

abbreviation

Meaning

Short for service level objective: an internal reliability target for a service, such as 99.9 percent of requests succeeding over 30 days.

Where you use it

Said letter by letter. An SLO is measured with an SLI (service level indicator), such as success rate or latency. The allowed failure, here 0.1 percent, is the 'error budget'; when it runs out, teams slow down releases.

Examples

1. Our SLO for the login API is 99.95 percent of requests under 300 milliseconds.

2. We missed the SLO this month, so the team will focus on reliability work.

Common phrases

set an SLO · meet the SLO · error budget · SLI

SRE

abbreviation

Meaning

Short for site reliability engineering: using software engineering methods to run production systems reliably. It also names the engineer who does this work.

Where you use it

Started at Google in the early 2000s. Key ideas are SLOs, error budgets, automation and reducing 'toil' (repetitive manual work). People say 'an SRE', 'the SRE team' and 'SRE practices'.

Examples

1. The SRE team owns the on-call process and the incident tooling.

2. She moved from backend development to SRE because she enjoys debugging production problems.

Usage note

DevOps is a broad culture; SRE is one concrete way to practise it, with clear targets such as SLOs.

Common phrases

SRE team · SRE practices · site reliability engineer · reduce toil

runbook

noun

Meaning

A written step-by-step guide for handling a specific task or alert, such as restarting a service or clearing a full disk, so anyone on call can follow it.

Where you use it

Good alerts link to a runbook. Teams write, update and automate runbooks. 'Playbook' is used in a similar way, often for broader incident procedures. Runbooks are kept in wikis or in the code repository.

Examples

1. Follow the runbook for this alert: check the queue, then restart the worker pods.

2. The runbook was out of date, so the on-call engineer lost twenty minutes.

Common phrases

follow the runbook · update the runbook · runbook link · automated runbook

framework

noun

Meaning

A ready-made structure for building applications that gives you rules, tools and common parts, so you only write the code that is specific to your product.

Where you use it

Teams choose, adopt, learn and migrate between frameworks such as React, Django, Spring or Laravel. Job ads list frameworks as required skills, and the framework often shapes how the whole project is organized.

Examples

1. We're moving the backend from Flask to a bigger framework like Django.

2. Which testing framework does the team use?

Common phrases

web framework · testing framework · choose a framework · framework version · migrate to a new framework

dependency

noun

Meaning

A library, service or other piece of software that your code needs in order to work, so a change or failure in it can affect your project.

Where you use it

Teams add, install, update, pin and remove dependencies, often listed in files such as package.json or requirements.txt. It is also used for tasks: 'This ticket has a dependency on the API work.'

Examples

1. Before adding a new dependency, check how well it is maintained.

2. The build broke because one of our dependencies released a new major version.

Common phrases

add a dependency · update dependencies · external dependency · dependency on · pin a dependency

tech stack

noun

Meaning

The set of programming languages, frameworks, databases and tools that a team uses to build and run a product.

Where you use it

Often shortened to 'stack': 'What's your stack?', 'Our stack is TypeScript, Node and Postgres.' It appears in job ads, interviews and architecture discussions. 'Full-stack developer' comes from the same idea.

Examples

1. Our tech stack is fairly standard: React on the front end and Go on the back end.

2. In the interview, they asked how I would choose a tech stack for a new product.

Common phrases

our tech stack · modern tech stack · choose a tech stack · full-stack developer

architecture

noun

Meaning

The high-level structure of a software system: its main parts, how they communicate with each other and the key technical decisions behind them.

Where you use it

Teams design, review, document and change their architecture. You will hear 'architecture diagram', 'architecture review', 'event-driven architecture' and 'This doesn't fit our architecture.'

Examples

1. Before we split the service, let's draw the current architecture on the whiteboard.

2. The architecture review flagged the single shared database as a risk.

Usage note

The 'ch' is pronounced like 'k': AR-ki-tek-cher.

Common phrases

software architecture · architecture diagram · architecture review · event-driven architecture · system architecture

design pattern

noun

Meaning

A proven, reusable solution to a common design problem in code, such as Singleton, Factory or Observer, described as a general approach rather than finished code.

Where you use it

Developers apply, recognize and sometimes overuse design patterns. In reviews you may hear 'This is basically the strategy pattern' or 'We don't need a pattern for something this simple.'

Examples

1. We used the adapter design pattern to support three payment providers behind one interface.

2. Learning the common design patterns makes large codebases much easier to read.

Common phrases

apply a design pattern · common design patterns · factory pattern · observer pattern

trade-off

noun

Meaning

A situation where getting more of one good thing means accepting less of another, such as speed versus accuracy or simplicity versus flexibility.

Where you use it

A key word in design discussions and interviews: 'What are the trade-offs?', 'It's a trade-off between cost and performance.' Senior engineers are expected to explain trade-offs, not just give one answer.

Examples

1. Caching makes the page faster, but the trade-off is that prices may be a minute out of date.

2. We chose the simpler design and accepted the trade-off in flexibility.

Usage note

Also written 'tradeoff', especially in American texts. The plural is 'trade-offs'.

Common phrases

make a trade-off · the trade-off between · accept a trade-off · weigh the trade-offs

scalable

adjective

Meaning

Able to handle more users, data or traffic by adding resources, without a complete redesign and without becoming much slower.

Where you use it

Used about systems, architectures and even team processes: 'a scalable solution', 'Will this scale?' The noun is 'scalability'. 'Scale up' means using bigger machines; 'scale out' means adding more machines.

Examples

1. The current setup works for 1,000 users, but it isn't scalable to a million.

2. Scalability was the main reason we moved image processing into a queue.

Common phrases

highly scalable · scalable architecture · scalable solution · scalability issues

microservices

noun

Meaning

An architecture in which an application is built as many small, independent services, each with one job, that talk to each other over the network.

Where you use it

Usually compared with a 'monolith', one large application. Teams 'move to microservices' or 'break the monolith into microservices'. Each microservice can be deployed and scaled on its own, but the whole system becomes harder to debug.

Examples

1. We split the monolith into six microservices over two years.

2. With microservices, one slow service can affect the whole checkout flow.

Common phrases

microservices architecture · move to microservices · break into microservices · a microservice

monolith

noun

Meaning

An application built and deployed as one single unit, where all features share the same codebase and usually the same database.

Where you use it

Often contrasted with microservices. A monolith is simpler to start with; problems appear when it grows and teams start blocking each other. People talk about 'breaking up the monolith' and a 'modular monolith'. The adjective is monolithic.

Examples

1. We're slowly moving the billing code out of the monolith into its own service.

2. For a team of four, a well-structured monolith is probably the right choice.

Usage note

'Monolith' is not negative by itself: many successful products run on a well-organized monolith.

Common phrases

break up the monolith · modular monolith · monolithic application · monolith vs microservices

modular

adjective

Meaning

Built from separate, independent parts with clear boundaries, so each part can be understood, tested, changed or replaced without touching the others.

Where you use it

A positive word in design discussions: 'a modular architecture', 'make the code more modular'. Each part is called a module. Modular code is easier to reuse and to divide among several teams.

Examples

1. The plugin system is modular, so customers can turn features on and off.

2. Let's make the reporting code more modular before the second team starts working on it.

Common phrases

modular design · modular architecture · more modular · modular monolith

abstraction

noun

Meaning

Hiding complex details behind a simpler interface, so you can use something without knowing how it works inside, like calling save() without knowing the database query.

Where you use it

Developers talk about 'a layer of abstraction', 'the right abstraction' and 'leaky abstractions', which fail to hide their details. Too many abstractions make code hard to follow, so reviewers sometimes say 'this abstraction isn't pulling its weight'.

Examples

1. The storage abstraction lets us switch from local files to S3 without touching the rest of the app.

2. Three layers of abstraction for one database call is too much.

Common phrases

layer of abstraction · leaky abstraction · the right abstraction · premature abstraction

separation of concerns

noun

Meaning

A design principle saying that each part of a program should handle one clear job, such as showing data, applying business rules or storing data, without mixing them.

Where you use it

Patterns such as MVC and layered architecture are ways to achieve it. Reviewers mention it when, for example, SQL queries appear inside UI code. Here a 'concern' means an area of responsibility, not a worry.

Examples

1. Putting the tax rules in the controller breaks separation of concerns; move them into a service.

2. Good separation of concerns made it easy to replace the old UI.

Common phrases

clear separation of concerns · violate separation of concerns · layered architecture · single responsibility

loose coupling

noun

Meaning

A design in which the parts of a system depend on each other as little as possible, so a change in one part rarely forces changes in the others.

Where you use it

The opposite is tight coupling. People say components are 'loosely coupled' or 'tightly coupled'. It is often paired with 'high cohesion', meaning the code inside each part belongs together. Interfaces, events and queues help achieve loose coupling.

Examples

1. Loose coupling between the order and email services means one can go down without breaking the other.

2. We aim for loose coupling, so modules talk to each other only through public interfaces.

Common phrases

loosely coupled · tight coupling · high cohesion, loose coupling · reduce coupling