English is the everyday language of web development: HTML elements, CSS properties, JavaScript APIs, HTTP status codes and browser error messages are all written in it, and so is almost every framework's documentation. Knowing these terms helps front-end, back-end and full-stack developers read documentation faster, search for solutions with the right words and talk clearly with designers, clients and international teams.
100 terms
11 topics
58 core terms
201 example sentences
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Web Fundamentals
front end
noun
Meaning
The part of a website or web app that users see and interact with in the browser, built mainly with HTML, CSS and JavaScript.
Where you use it
Used in job titles, team names and planning meetings. Before a noun it is written with a hyphen (front-end developer, front-end code); many companies simply write frontend as one word.
Examples
The API is ready, but the front end still shows the old prices.
We're hiring two front-end developers who know React.
Usage note
Front end (noun), front-end (adjective) and frontend are all common; just be consistent within one document.
Common phrases
front-end developer · front-end code · work on the front end · front-end framework
The server side of a website or app that users do not see: it stores data, runs business logic and sends the front end what it needs.
Where you use it
Back-end developers work with servers, databases and APIs, using languages and platforms such as PHP, Python, Java, C#, Go and Node.js. As with front end, the hyphen appears before a noun: back-end service, back-end team.
Examples
The page is slow because the back end takes three seconds to answer.
She moved from front-end work to the back-end team last year.
Common phrases
back-end developer · back-end service · on the back end · back-end logic
A program such as Chrome, Firefox, Safari or Edge that downloads web pages and turns their code into the screens people read and use.
Where you use it
Developers test their work in several browsers and talk about browser support, browser bugs and browser extensions. 'In the browser' often means 'on the client side', as opposed to on the server.
Examples
It works in Chrome. Which browser are you using?
Clear your browser cache and reload the page.
This code runs in the browser, so never put secret keys in it.
Common phrases
browser support · browser extension · browser cache · open in a browser · modern browsers
Uniform Resource Locator: the full address of a page or file on the web, such as https://example.com/blog?page=2.
Where you use it
Usually said letter by letter. Developers talk about the parts of a URL (protocol, domain, path, query string and fragment) and say things like 'paste the URL' or 'the URL changes when you filter'.
Examples
Can you send me the URL of the page where you see the error?
Keep the search filters in the URL so users can share the results.
Usage note
Some developers pronounce URL as one word, 'earl', but saying it letter by letter is the safer choice in meetings.
A computer or program that waits for requests from browsers and other clients and sends back pages, files or data.
Where you use it
The word means both the machine and the software running on it. Developers start, restart and deploy to servers, and say things like 'the server is down' or 'it works on my local server'.
Examples
The server is down again, so nobody can log in.
Run npm run dev to start the local server on port 3000.
Common phrases
start the server · web server · local server · server error · the server is down
The side of a connection that asks for data, usually the browser or a mobile app, as opposed to the server that answers.
Where you use it
Common in 'client side', 'client-side code' and 'client-server model'. In agency work 'client' also means the customer who pays for the website, so the context decides the meaning.
Examples
We validate the form on the client and again on the server.
Move this calculation to the client side so the server has less work.
Common phrases
client side · client-side code · client-server model · API client
An application that runs in a web browser instead of being installed on the device, such as online email, maps or a project management tool.
Where you use it
Short for web application. Developers often contrast a web app (interactive, with logins and data) with a website (mostly content). A progressive web app (PWA) can also be installed and can work offline.
Examples
It started as a simple website and grew into a full web app with user accounts.
Our web app works on any device with a modern browser.
Common phrases
build a web app · progressive web app · web app development · single-page web app
Tools built into browsers that let developers inspect HTML and CSS, debug JavaScript, watch network requests and measure performance.
Where you use it
Usually opened with F12 or with right-click and Inspect. People call them dev tools or DevTools and refer to the panels by name: Elements, Console, Network, Sources and Performance.
Examples
Open the developer tools and check the Console for errors.
I used the browser's developer tools to test the page on a small screen.
Common phrases
open the developer tools · browser developer tools · Network tab · inspect an element
Working the same way in different browsers, such as Chrome, Firefox, Safari and Edge, and in their different versions and on different devices.
Where you use it
Mostly heard in 'cross-browser testing' and 'cross-browser compatibility'. Developers check browser support on the Can I use website and add fallbacks or polyfills for older browsers.
Examples
We need a day of cross-browser testing before the launch.
This cross-browser bug only appears in Safari on iOS.
HyperText Markup Language: the standard language for describing the structure and content of a web page, such as headings, paragraphs, links and images.
Where you use it
Said letter by letter. Developers write and validate HTML and talk about HTML files, HTML templates and the HTML a framework outputs. People still say HTML5, although the standard is now simply updated as the HTML Living Standard.
Examples
Can you check the HTML? The button is outside the form.
The server returns plain HTML, so the page loads fast even without JavaScript.
Usage note
HTML is a markup language, not a programming language: it describes content but has no logic such as loops or conditions.
Common phrases
write HTML · valid HTML · HTML file · HTML template · HTML element
A single building block of an HTML page, such as a paragraph, image or button, usually written as an opening tag, content and a closing tag.
Where you use it
Used constantly in HTML, CSS and JavaScript: you select, style, hide, create and remove elements. Browser developer tools let you 'inspect element' to see its code and styles.
Examples
Right-click the button and choose Inspect to see which element is on top.
The script creates a new list element for every comment.
Usage note
A tag is the code in angle brackets (<p>); an element is the whole thing, from the opening tag to the closing tag, including its content.
Common phrases
HTML element · inspect element · parent element · child element · create an element
A piece of HTML code in angle brackets, such as <h1> or </p>, that marks where an element starts or ends.
Where you use it
Developers talk about opening and closing tags, tags without a closing pair such as <img>, and specific ones like the title tag, meta tags and script tags. Outside HTML, 'tag' can also mean a label on a blog post or a version marker in Git.
Examples
You forgot the closing tag, so the whole footer is inside the link.
Add the script tag at the end of the body.
Common phrases
opening tag · closing tag · script tag · self-closing tag · title tag
Extra information written inside an opening HTML tag as a name and a value, such as href in a link or alt in an image.
Where you use it
You add, set, remove and read attributes. Common ones are id, class, href, src, alt and type; custom data-* attributes store your own values for JavaScript.
Examples
The image has no alt attribute, so screen readers may read out the file name instead.
Store the product ID in a data attribute on the button.
Usage note
Watch the stress: the noun is AT-tri-bute, the verb (to attribute something to someone) is at-TRI-bute. In CSS the matching word is property, not attribute.
Common phrases
add an attribute · alt attribute · data attribute · attribute value · boolean attribute
An HTML attribute that gives an element one or more names, so that CSS and JavaScript can find and style a group of elements together.
Where you use it
You add, remove and toggle classes, and select them in CSS with a dot (.card). Naming systems such as BEM and utility-class frameworks such as Tailwind are built around classes. In JavaScript, class is also a keyword for object-oriented code.
Examples
Add an active class to the current menu item.
The button has five utility classes, but none of them sets the color.
Common phrases
add a class · toggle a class · class name · class selector · utility class
A title for a page or section, marked up with the elements h1 to h6, where h1 is the main title and the others show lower levels.
Where you use it
Headings form the outline of a page for screen readers and search engines, so developers keep a logical heading order and avoid skipping levels just to get a smaller font size.
Examples
Each page should have one main heading in an h1.
The section headings jump from h2 to h5, so the outline is confusing.
Usage note
A heading (h1–h6) is title text. A header is something else: the <header> element at the top of a page or section, or an HTTP header.
Clickable text or an image that takes the user to another page or place, created in HTML with the a element and its href attribute.
Where you use it
Also a verb: 'link to the pricing page'. Developers talk about internal and external links, broken links and link text; the full word 'hyperlink' appears mostly in formal writing.
Examples
There are twelve broken links in the old blog posts.
Use a link for navigation and a button for actions.
Usage note
'Click here' is weak link text: screen-reader users and search engines get more from link text that says where the link goes.
Common phrases
broken link · internal link · link text · click a link · link to a page
A part of a page where users enter information, such as a login, search or contact form, which is then sent to a server.
Where you use it
Developers build, validate and submit forms and handle form errors. Good forms have a label for every field, clear error messages and the right input types, such as email or tel.
Examples
The contact form sends the message, but the user never sees a confirmation.
We validate the form in the browser first and then again on the server.
Common phrases
submit a form · form validation · contact form · form field · login form
A box or control in a form where a user types or selects a value, such as a name, an email address, a password or a date.
Where you use it
Created mostly with the input element and its type attribute (text, email, password, checkbox, date). Developers often just say 'input' or 'field', and talk about placeholders, labels and required fields.
Examples
The phone input field should only accept numbers.
Every input field needs a visible label, not just placeholder text.
Common phrases
text input field · required field · input type · placeholder text · field label
HTML that uses elements according to their meaning, such as nav, main, article and button, instead of generic div and span elements for everything.
Where you use it
Comes up in code reviews and accessibility work: semantic HTML gives screen readers, search engines and browsers useful information for free. Its opposite is jokingly called 'div soup'.
Examples
Replace the clickable div with a real button; semantic HTML gives you keyboard support for free.
Good semantic HTML makes the page easier to style and easier to test.
Common phrases
semantic elements · semantic markup · landmark elements · div soup
Cascading Style Sheets: the language that controls how HTML looks, including colors, fonts, spacing, layout and animations.
Where you use it
Said letter by letter. You write, add and override CSS, and work with CSS files, CSS frameworks such as Tailwind or Bootstrap, and CSS-in-JS libraries. 'Cascading' refers to the rules that decide which style wins.
Examples
I fixed the alignment with three lines of CSS.
Our CSS is getting messy, so we're moving to Tailwind.
The part of a CSS rule that says which elements the styles apply to, for example p, .button or #header.
Where you use it
Developers write, combine and simplify selectors, and the same selectors are used in JavaScript with querySelector(). Common types are element, class, ID, attribute and pseudo-class selectors.
Examples
This selector is too specific; just use the class name.
The test fails because the selector no longer matches any element.
Common phrases
CSS selector · class selector · ID selector · match a selector · complex selector
An approach to building pages so that the same layout adapts to any screen size, from phones and tablets to large monitors.
Where you use it
Built with flexible layouts, relative units, flexible images and media queries. People say a site 'is responsive' or 'isn't responsive', and 'mobile-first' means designing for small screens first.
Examples
The client wants a responsive design that works well on phones too.
With responsive design, we don't need a separate mobile site anymore.
In CSS, the name of a style feature you set, such as color, margin or display, which is always paired with a value.
Where you use it
A CSS declaration has the form 'property: value;'. Developers set, change and override properties; custom properties (CSS variables such as --main-color) store reusable values. JavaScript objects have properties too.
Examples
Which CSS property makes the text bold? It's font-weight.
Use a custom property for the brand color so we can change it in one place.
Usage note
In English, HTML elements have attributes and CSS rules have properties. Turkish speakers often mix them up because both can be translated as 'özellik'.
Common phrases
CSS property · custom property · set a property · shorthand property
A file or block of CSS rules that describes how a page should look; most sites link to one or more external .css files.
Where you use it
You link, load or import a stylesheet, usually with a <link> tag in the head. Browsers also have their own default (user agent) stylesheets, which is why projects often add a reset or normalize file.
Examples
The page looks unstyled because the stylesheet returns a 404.
Load the print stylesheet only when the user prints the page.
Common phrases
link a stylesheet · external stylesheet · global stylesheet · print stylesheet
The way elements are arranged on a page: where columns, menus, images and text sit and how they move when the screen size changes.
Where you use it
Developers build, fix and test layouts, and say a layout 'breaks', 'shifts' or 'overflows'. The main CSS layout methods are flexbox, grid and positioning.
Examples
The layout breaks on screens narrower than 360 pixels.
We'll use a two-column layout on desktop and a single column on mobile.
Usage note
The noun is one word (layout); the verb is two words: 'lay out the cards in a grid'.
Common phrases
page layout · two-column layout · the layout breaks · layout shift · fix the layout
A CSS layout method for arranging items in a single row or column and controlling how they grow, shrink, align and share space.
Where you use it
Turned on with display: flex. The official name is the Flexible Box Layout Module, but everyone says flexbox. Common properties are justify-content, align-items, gap and flex-wrap.
Examples
Use flexbox to center the icon and the text inside the button.
The cards wrap onto a new line because the flexbox container has flex-wrap set.
Usage note
A common rule of thumb: flexbox for one dimension (a row or a column), grid for two dimensions (rows and columns together).
A CSS layout system for placing elements in rows and columns at the same time, useful for full page layouts and card galleries.
Where you use it
Turned on with display: grid. Developers define columns and rows (grid-template-columns), use the fr unit and name grid areas. Often just called 'grid': 'Let's do this with grid.'
Examples
With CSS grid, the gallery shows four columns on desktop and two on tablets.
I rebuilt the dashboard with CSS grid and removed half of the wrapper divs.
Common phrases
grid layout · grid template · grid area · fr unit · display: grid
A CSS rule that applies styles only when a condition is true, such as a minimum screen width, dark mode or printing.
Where you use it
Written with @media, for example @media (min-width: 768px). Media queries are the main tool of responsive design; developers write and adjust them for each breakpoint.
Examples
Add a media query so the sidebar moves under the content on mobile.
This media query switches the colors when the user prefers dark mode.
Common phrases
write a media query · min-width media query · print media query · prefers-color-scheme
The CSS idea that every element is a rectangular box made of content, padding, border and margin, which together decide its size and spacing.
Where you use it
Comes up when sizes look wrong. Many projects set box-sizing: border-box so that the width includes padding and border. Browser developer tools show the box model of the selected element.
Examples
The card is 20 pixels wider than expected; check the box model in DevTools.
Once you understand the box model, spacing in CSS makes much more sense.
Common phrases
CSS box model · box-sizing · border-box · content box
The space outside an element's border, which pushes other elements away from it.
Where you use it
Set with margin or with margin-top, margin-right and so on. 'margin: 0 auto' is a classic way to center a block. Vertical margins between blocks can collapse into one, which surprises many beginners.
Examples
Remove the bottom margin from the last paragraph.
There's too much margin between the title and the image.
Usage note
Margin is outside the border; padding is inside it. An easy way to remember: padding is like the padding inside a jacket.
The space inside an element, between its content and its border, which keeps the content away from the edges.
Where you use it
Set with padding or with padding-top, padding-left and so on. Padding shows the element's background color, while margin is always transparent. Buttons and cards almost always need some padding.
Examples
Give the button more padding so it's easier to tap on a phone.
The text touches the edge of the card because the padding is zero on mobile.
A screen width at which a responsive layout changes, for example from one column on phones to three columns on desktops.
Where you use it
Defined with media queries, often at widths such as 640, 768 or 1024 pixels, though many teams place breakpoints where their content needs them. Designers and developers agree on a shared set of breakpoints.
Examples
At the tablet breakpoint the menu turns into a hamburger icon.
We only have three breakpoints: mobile, tablet and desktop.
Usage note
In debugging, a breakpoint means something else: a line where the debugger pauses the code.
Common phrases
mobile breakpoint · add a breakpoint · breakpoint system · at the desktop breakpoint
The visible area of a web page inside the browser window or phone screen, which changes size when the window is resized or the phone is rotated.
Where you use it
Responsive pages need the viewport meta tag (width=device-width, initial-scale=1). The CSS units vw and vh are percentages of the viewport's width and height, and 'above the fold' means inside the first viewport.
Examples
Without the viewport meta tag, the phone shows a tiny desktop version of the page.
The hero image should fill the whole viewport on desktop.
Common phrases
viewport meta tag · viewport width · small viewports · fill the viewport
The rule CSS uses to decide which style wins when several rules target the same element: ID selectors beat class selectors, which beat element selectors.
Where you use it
Comes up whenever 'my CSS isn't working'. Developers talk about high or low specificity, 'specificity wars' and overriding with !important, which is usually seen as a last resort. Inline styles beat rules in stylesheets.
Examples
Your rule doesn't apply because the theme's selector has higher specificity.
Keep specificity low so components are easy to override.
Usage note
A hard word to say: spe-si-FI-si-ty, with the stress on the third syllable.
Common phrases
high specificity · specificity war · increase specificity · override with !important
The programming language that runs in every web browser and makes pages interactive; with Node.js it also runs on servers.
Where you use it
Often shortened to JS in speech and file names (app.js). Developers write, load, bundle and minify JavaScript; 'vanilla JavaScript' means plain JavaScript without a framework.
Examples
The menu doesn't open because a JavaScript error stops the script.
We built the first version in vanilla JavaScript, without any framework.
Usage note
JavaScript has nothing to do with Java except part of its name. Its official standard is called ECMAScript (ES2015, ES2024 and so on).
Document Object Model: the tree of objects a browser builds from a page's HTML, which JavaScript can read and change while the page is open.
Where you use it
Pronounced as one word, 'dom'. Developers update, query and manipulate the DOM; frameworks such as React use a 'virtual DOM' to work out what to change on the page.
Examples
The script runs before the DOM is ready, so it can't find the button.
Avoid changing the DOM directly when you use React.
Common phrases
update the DOM · DOM element · DOM tree · virtual DOM · manipulate the DOM
A ready-made set of code, tools and rules for building applications, such as Angular, Vue, Next.js or Laravel, that shapes how a project is organized.
Where you use it
Developers choose, learn, migrate between and sometimes 'fight with' frameworks. Front-end frameworks run in the browser; back-end frameworks such as Express, Django or Laravel run on the server.
Examples
Which framework are you using for the new dashboard?
We moved the blog to a static site framework, and it loads much faster now.
Usage note
A library is code you call; a framework calls your code and sets the structure. React describes itself as a library, but many people still call it a framework.
A collection of ready-made code that you add to a project and call when you need it, for example for dates, charts or animations.
Where you use it
Developers install, import, update and replace libraries, often through npm. People describe a library as lightweight, well-maintained or abandoned, and talk about third-party libraries.
Examples
We're using a charting library instead of drawing the graphs ourselves.
That library hasn't been updated in three years, so let's find another one.
A reusable, self-contained piece of a user interface, such as a button, modal or product card, with its own markup, styles and logic.
Where you use it
Central to React, Vue, Angular and Svelte. Developers create, reuse, render and split components, pass data to them as props, and build component libraries or design systems.
Examples
This page is too big; let's split it into smaller components.
The Button component accepts a size prop: small, medium or large.
Something that happens in the browser and that code can react to, such as a click, a key press, a form submission or the page finishing loading.
Where you use it
Developers listen for, handle, fire and prevent events. Common phrases are 'click event', 'event handler' and event.preventDefault(), which stops the browser's default action.
Examples
The click event fires twice because the listener was added twice.
Call preventDefault() on the submit event so the page doesn't reload.
Common phrases
click event · event handler · fire an event · handle an event · custom event
A function that waits for a specific event on an element, such as a click or a key press, and runs when that event happens.
Where you use it
Added with addEventListener() and removed with removeEventListener(). Forgotten listeners can cause memory leaks or code that runs twice. 'Event handler' is used for almost the same idea.
Examples
Add one event listener to the form instead of one to every input.
The modal closes twice because two event listeners are attached.
Common phrases
add an event listener · remove an event listener · attach a listener · scroll listener
Describes code that starts a task, such as loading data, and goes on running other code instead of waiting for that task to finish.
Where you use it
Often shortened to async, which is also a JavaScript keyword: async functions use await to pause until a promise settles. Network requests, timers and file reads are typical asynchronous operations.
Examples
The data is undefined because the request is asynchronous and hasn't finished yet.
Wrap the asynchronous call in try/catch so you can show an error message.
Usage note
The opposite is synchronous: code that runs line by line and waits for each step to finish.
Common phrases
asynchronous code · asynchronous request · async function · async/await
A JavaScript object that stands for a result that is not ready yet, such as data from a server, and that later succeeds or fails.
Where you use it
A promise is first pending, then fulfilled (resolved) or rejected. Developers handle it with .then() and .catch() or with async/await, and say that a function 'returns a promise'.
Examples
fetch() returns a promise, so you need await before you can read the data.
One of the promises was rejected, so Promise.all failed.
Common phrases
return a promise · resolve a promise · rejected promise · unhandled promise rejection
To turn code and data into what the user sees, either in the browser, which draws the page, or on the server, which builds the HTML.
Where you use it
Used for browsers (the page renders), frameworks (a component renders or re-renders) and servers (server-side rendering, SSR). 'Too many re-renders' is a common React performance complaint.
Examples
The list renders five hundred items at once, which makes scrolling slow.
This component re-renders every time the parent's state changes.
Common phrases
render a component · re-render · server-side rendering · render on the server · render-blocking
The data an app or component holds at a given moment, such as whether a menu is open or what a user has typed, which controls what is shown.
Where you use it
Developers set, update, share and reset state, and 'lift state up' to a parent component. Global state is shared across the app, often with a state management library; local state belongs to one component. When state changes, the UI re-renders.
Examples
Keep the filter values in state so the list updates when they change.
The cart count is wrong because two components keep their own copy of the state.
Common phrases
update state · global state · local state · state management · lift state up
A web app that loads one HTML page and then updates the content with JavaScript as the user moves around, instead of loading a new page each time.
Where you use it
Usually shortened to SPA. SPAs feel fast after the first load but need extra work for SEO, the back button and initial load time, so many teams now combine them with server rendering.
Examples
Our admin panel is a single-page application built with Vue.
Since it's a single-page application, the browser never does a full reload.
The standard package manager for JavaScript and the online registry it installs packages from, used through commands such as npm install.
Where you use it
Said letter by letter and written in lowercase. Developers install, update and publish packages with npm and run project scripts with npm run. Alternatives such as pnpm and Yarn use the same registry.
Examples
Run npm install after you pull, because the dependencies have changed.
This package has two million weekly downloads on npm.
Usage note
It is often expanded as 'Node Package Manager', but the project itself says that npm is not officially an acronym.
Common phrases
npm install · npm package · npm run build · publish to npm
An outside package or library that a project needs in order to work, listed in a file such as package.json.
Where you use it
Developers add, install, update, pin and remove dependencies. Dev dependencies are needed only during development, and outdated dependencies are a common source of security warnings from npm audit.
Examples
This project has over a thousand dependencies once you count the nested ones.
Let's update the dependencies before we start the new feature.
A programming language built on JavaScript that adds types, so that many errors are found while you write the code instead of when it runs.
Where you use it
Created by Microsoft and widely used with React, Angular, Vue and Node.js. TypeScript is compiled to plain JavaScript; developers talk about types, interfaces, type errors and strict mode.
Examples
TypeScript caught the bug: we were passing a string where a number was expected.
We're slowly moving the old JavaScript files to TypeScript.
Common phrases
written in TypeScript · TypeScript types · type error · migrate to TypeScript
A tool that combines many JavaScript, CSS and other files and their dependencies into a few optimized files that browsers can load quickly.
Where you use it
Well-known bundlers and build tools include webpack, Rollup, esbuild and Vite. The output is called a bundle; developers talk about bundle size, code splitting and tree shaking (removing unused code).
Examples
The bundler puts the whole chart library into the main file, which is why it's so large.
We replaced our old bundler with Vite, and the dev server now starts in a second.
Hypertext Transfer Protocol: the set of rules that browsers and servers use to send requests and responses across the web.
Where you use it
Developers speak of HTTP requests, methods, headers and status codes. Versions are named HTTP/1.1, HTTP/2 and HTTP/3; the secure version, used by almost every site today, is HTTPS.
Examples
The app sends an HTTP request to the server every time you press Save.
Our CDN already serves everything over HTTP/2.
Common phrases
HTTP request · HTTP response · HTTP header · HTTP status code · over HTTP
Application Programming Interface: a defined way for one piece of software to ask another for data or actions, for example a web API that returns JSON.
Where you use it
Said letter by letter. In web work it usually means an HTTP API on a server, but browser features such as the Fetch API or the Geolocation API are also called APIs. Developers call, consume, build and document APIs.
Examples
The front end calls the API to get the latest orders.
Is the API documented, or do I have to read the code?
Common phrases
call an API · public API · API key · API documentation · third-party API
A message a client sends to a server asking for something, such as a web page, an image or data, or asking it to save a change.
Where you use it
Developers send, make, handle and block requests, and check them in the Network tab of the developer tools. Each HTTP request has a method, a URL, headers and sometimes a body.
Examples
The page sends forty requests on load; can we combine some of them?
Check the request in the Network tab and see what the server returned.
Usage note
As a verb it takes a direct object: 'request data', not 'request for data'. The noun is followed by for: 'a request for data'.
Common phrases
send a request · handle a request · GET request · request body · failed request
The message a server sends back after a request, with a status code, headers and usually a body such as HTML or JSON.
Where you use it
Developers talk about response time, response headers and the response body, and say that an API 'returns' or 'sends back' a response. A slow response is one of the most common performance complaints.
Examples
The response is empty, but the status code is 200.
Average response time went up after the last deploy.
Common phrases
response time · response body · response headers · return a response · JSON response
JavaScript Object Notation: a simple text format for data, made of keys and values in curly braces, used by most web APIs.
Where you use it
Pronounced like the name Jason. APIs return or accept JSON; in JavaScript you parse it with JSON.parse() and create it with JSON.stringify(). Configuration files such as package.json use it as well.
Examples
The endpoint returns the product list as JSON.
The app crashed because the server sent HTML instead of valid JSON.
A specific URL of an API that accepts requests for one kind of data or action, such as /api/users or /api/orders/42.
Where you use it
Developers create, call, expose, deprecate and protect endpoints, and usually name them together with a method: 'the POST /login endpoint'. API documentation lists every endpoint with its parameters.
Examples
We need a new endpoint that returns only active users.
That endpoint is deprecated; use /v2/orders instead.
Common phrases
API endpoint · call an endpoint · expose an endpoint · protected endpoint · deprecated endpoint
A three-digit number in every HTTP response that shows the result, such as 200 for success, 404 for not found or 500 for a server error.
Where you use it
Codes are grouped: 2xx success, 3xx redirects, 4xx client errors and 5xx server errors. Developers say a request 'returns a 404' or 'is throwing 500s', and read the numbers aloud as 'four-oh-four' and 'five hundred'.
Examples
The API returns status code 401 when the token has expired.
Log every request with its status code and response time.
Common phrases
return a status code · HTTP status code · 404 error · 500 error · success status code
To request and receive data from a server or API, for example the latest messages or a list of products, often while the page is already open.
Where you use it
In JavaScript, fetch() is also the name of the built-in function for HTTP requests (the Fetch API). Developers fetch data on page load, on scroll or after a click, and talk about 'data fetching' strategies.
Examples
We fetch the user's profile as soon as they log in.
The component fetches new comments every thirty seconds.
Common phrases
fetch data · fetch from an API · data fetching · refetch
An API built in the REST style, where each resource has its own URL and standard HTTP methods such as GET, POST and DELETE act on it.
Where you use it
REST stands for Representational State Transfer and is pronounced as one word, 'rest'. People also say 'RESTful API'. GraphQL is a common alternative style.
Examples
The mobile app and the website both use the same REST API.
In our REST API, GET /orders lists orders and POST /orders creates a new one.
Common phrases
RESTful API · REST endpoint · design a REST API · call a REST API
The word at the start of an HTTP request that says what the client wants to do, such as GET to read, POST to create or DELETE to remove.
Where you use it
The common methods are GET, POST, PUT, PATCH and DELETE, also called HTTP verbs. Developers say 'send a POST request' or 'this endpoint only accepts GET'.
Examples
The server returns 405 because we used the wrong HTTP method.
Use PATCH as the HTTP method when you only change a few fields.
Usage note
PUT usually replaces a whole resource, while PATCH changes only part of it.
Common phrases
GET request · POST request · HTTP verb · method not allowed
A name and value pair sent with an HTTP request or response that carries extra information, such as Content-Type, Authorization or Cache-Control.
Where you use it
Developers set, read and check headers, often in the Network tab. Security, caching and CORS all depend on headers. In HTML, header is also the name of the element at the top of a page or section.
Examples
Send the token in the Authorization header, not in the URL.
The response headers show that the file is cached for a year.
Common phrases
request header · response header · set a header · Authorization header · security headers
An organized store of data, such as users, orders or posts, that a back end can save to, search and update quickly.
Where you use it
Web projects use relational databases such as PostgreSQL and MySQL, which are queried with SQL, or NoSQL databases such as MongoDB. Developers query, migrate, back up and seed a database.
Examples
The page is slow because it hits the database thirty times per request.
Please don't run tests against the production database.
Common phrases
query the database · database migration · relational database · database backup · production database
A small piece of data that a website stores in the browser and that is sent back with later requests, used for logins, settings and tracking.
Where you use it
Servers set cookies with the Set-Cookie header; important attributes are HttpOnly, Secure and SameSite. Privacy rules in the EU and other regions are the reason many sites show a cookie banner asking for consent.
Examples
The session cookie is HttpOnly, so JavaScript can't read it.
Users stay logged in because we store a cookie for thirty days.
Common phrases
set a cookie · session cookie · third-party cookies · cookie banner · clear cookies
The period during which a server remembers a logged-in user, usually through an ID stored in a cookie, until the user logs out or the session expires.
Where you use it
Developers create, store, expire and destroy sessions, and talk about session timeouts. The browser's sessionStorage API is a different thing: data kept only while the tab is open.
Examples
Your session has expired. Please log in again.
We store sessions in Redis so that all servers can share them.
Common phrases
session cookie · session timeout · session expired · end a session · session ID
Happening on the server rather than in the user's browser, for example server-side code, validation or rendering.
Where you use it
Written with a hyphen before a noun (server-side rendering) and as two words after a preposition (on the server side). Its opposite is client-side. Server-side rendering is often shortened to SSR.
Examples
Never trust client input; always do server-side validation as well.
We switched to server-side rendering to make the first load faster.
Common phrases
server-side rendering · server-side validation · server-side code · on the server side
A named setting, such as a database URL or an API key, that is given to an app from outside the code so that it can differ between environments.
Where you use it
Often kept in a .env file during development and set in the hosting dashboard for staging and production. Developers read, set and rotate them; .env files with secrets are normally kept out of Git.
Examples
The build fails because the API_URL environment variable is missing.
Put the payment key in an environment variable, not in the source code.
Common phrases
set an environment variable · .env file · missing environment variable · env vars
The readable address of a website, such as example.com, which people type instead of a numeric IP address.
Where you use it
You register, buy, renew, transfer and point a domain name, usually through a registrar and for a yearly fee. In speech people mostly just say 'domain'.
Examples
Did anyone renew the domain name? The site is showing a parking page.
We bought the domain name last week, but it isn't pointing to our server yet.
Common phrases
register a domain name · renew a domain · custom domain · point a domain to
A service that keeps a website's files and code on servers connected to the internet, so that people can visit the site at any time.
Where you use it
Types include shared hosting, VPS, dedicated servers, cloud hosting and platforms such as Vercel or Netlify for front-end projects. People compare hosting providers and plans; the verb is 'host': 'We host it on AWS.'
Examples
The site goes down every evening; maybe it's time to change our hosting.
Shared hosting is fine for a small company website.
Common phrases
web hosting · shared hosting · hosting provider · cloud hosting · hosting plan
To put a new version of a website or app on a server so that users can reach it, usually through an automated process.
Where you use it
You deploy code, a branch or an app to staging or production. The noun is deployment, often shortened to 'deploy' in speech: 'the last deploy broke the checkout'.
Examples
We don't deploy on Fridays.
I deployed the fix to staging. Can you test it there?
Common phrases
deploy to production · deploy a fix · automatic deployment · roll back a deploy
A digital file installed on a server that proves the site's identity and lets the browser set up an encrypted HTTPS connection.
Where you use it
Certificates are issued by certificate authorities, including the free Let's Encrypt, and they expire, so they must be renewed. An expired certificate causes a full-page browser warning, a common cause of sudden outages.
Examples
Our SSL certificate expires next week. Is auto-renewal turned on?
The hosting panel installs a free SSL certificate for every domain.
Usage note
Modern sites actually use TLS, the newer protocol that replaced SSL, but most people and hosting panels still say 'SSL certificate'.
Common phrases
install an SSL certificate · renew a certificate · expired certificate · certificate authority · wildcard certificate
Domain Name System: the internet's directory that translates domain names like example.com into the IP addresses of servers.
Where you use it
Developers edit DNS records, such as A, CNAME, MX and TXT, at their registrar or DNS provider. Changes can take time to spread, so people say 'wait for DNS to propagate'.
Examples
I updated the DNS records an hour ago, but some users still see the old site.
Add a CNAME record in your DNS settings to connect the custom domain.
Common phrases
DNS record · DNS propagation · DNS provider · update DNS settings
The automatic step that turns source code into files ready for production, for example by compiling, bundling and minifying them; also the result of that step.
Where you use it
Also a verb: build the project. Developers say 'the build failed', 'the build is green' and 'run a production build', usually with npm run build. CI servers run a build for every change.
Examples
The build failed because of a type error on the checkout page.
A production build takes about four minutes on our CI server.
Common phrases
the build failed · production build · build step · run a build · build time
Software, such as Nginx or Apache, that accepts HTTP requests and serves web pages and files; the term is also used for the machine that runs it.
Where you use it
Developers configure, restart and tune web servers, often placing Nginx in front of an application server as a reverse proxy. Typical tasks include redirects, compression and SSL settings.
Examples
The redirect is set up in the web server config, not in the app.
After you change the config, reload the web server.
Usage note
Nginx is pronounced 'engine x'.
Common phrases
configure a web server · reverse proxy · web server logs · restart the web server
A copy of the live site, set up as close to production as possible, where new versions are tested before real users see them.
Where you use it
Usually just called staging. A typical flow is development, then staging, then production. People say 'deploy to staging', 'it works on staging' and 'staging is down'.
Examples
The new checkout is on the staging environment; please test it before Thursday.
The staging environment uses a copy of last week's database.
Usage note
Production (often 'prod') is the live environment that real users see.
Common phrases
deploy to staging · staging server · staging and production · staging URL
How long a page takes to download and appear on screen in a usable state, usually measured in seconds or milliseconds.
Where you use it
Teams measure, reduce and monitor page load time, often with Lighthouse or with data from real users. Because 'loaded' can mean many things, developers now prefer specific metrics such as Largest Contentful Paint.
Examples
After we compressed the images, load time dropped from four seconds to under two.
Mobile load time matters more because most of our visitors use phones.
Common phrases
page load time · reduce load time · fast load time · measure load time
A place where copies of files or data are kept for a while so they can be served again faster, for example in the browser, on a CDN or on the server.
Where you use it
Also a verb: to cache a response. Developers clear and invalidate caches and set Cache-Control headers. 'It's a cache issue' is a typical answer when users still see an old version.
Examples
Users still see the old logo because it's in their browser cache.
We cache the product list for five minutes to reduce database load.
Usage note
Pronounced exactly like 'cash', not 'catch' or 'cash-ay'.
Common phrases
clear the cache · browser cache · cache invalidation · cache headers · hard refresh
Content Delivery Network: a network of servers around the world that stores copies of a site's files and delivers them from the location closest to each user.
Where you use it
Cloudflare, Fastly, Akamai and Amazon CloudFront are well-known CDNs. Developers put images, scripts and even whole pages behind a CDN and purge the CDN cache after a release.
Examples
Images load slowly in Asia because we don't use a CDN yet.
Purge the CDN cache, or users will keep getting the old file.
Common phrases
serve from a CDN · CDN cache · purge the CDN · edge server
A technique that waits to load images, videos or code until they are actually needed, for example when the user scrolls near them.
Where you use it
For images and iframes it can be as simple as loading="lazy". In JavaScript apps, routes and components are lazy-loaded with dynamic import(). Images at the top of the page are usually not lazy-loaded, because that would delay the main content.
Examples
Lazy loading the product images cut the initial page weight in half.
The admin pages use lazy loading, so normal users never download that code.
To make code files smaller by removing spaces, comments and line breaks and by shortening names, without changing how the code works.
Where you use it
Build tools minify JavaScript, CSS and HTML automatically for production. Minified files often end in .min.js, and source maps let developers debug minified code.
Examples
Is the CSS minified in production? The file is 300 KB.
The error is hard to read because the code is minified; turn on source maps.
Usage note
Minifying is not the same as compressing: compression (gzip or Brotli) is done by the server when it sends the files, and the two are usually used together.
Making image files as small as possible while they still look good, for example by compressing and resizing them and by using modern formats.
Where you use it
Covers modern formats such as WebP and AVIF, responsive images with srcset, correct dimensions and lazy loading. Many frameworks and CDNs offer automatic image optimization.
Examples
Image optimization alone made the home page twice as fast.
Editors upload 5 MB photos, so we need image optimization in the upload step.
Usage note
British English often writes optimisation, but code, tools and most documentation use the American spelling, optimization.
Three metrics from Google that measure real user experience on a page: loading (LCP), responsiveness (INP) and visual stability (CLS).
Where you use it
LCP is Largest Contentful Paint, INP is Interaction to Next Paint (it replaced FID in 2024) and CLS is Cumulative Layout Shift. Teams track them in Search Console and PageSpeed Insights; they are one of many signals Google uses in ranking.
Examples
Our Core Web Vitals failed on mobile because of a large layout shift in the header.
After the redesign, all three Core Web Vitals are in the green.
Common phrases
pass Core Web Vitals · Core Web Vitals report · layout shift · field data
The practice of making websites usable by everyone, including people who are blind or deaf, have limited movement or use assistive technology.
Where you use it
Often written a11y (a, eleven letters, y). Teams run accessibility audits and test against WCAG, the Web Content Accessibility Guidelines. In many countries, accessibility is also a legal requirement for some websites.
Examples
We ran an accessibility audit and found forty issues on the checkout page.
Good accessibility also helps users on slow phones or in bright sunlight.
A short written description of an image, added with the alt attribute, that screen readers read aloud and browsers show if the image fails to load.
Where you use it
Developers and editors write, add and check alt text. Purely decorative images get an empty alt (alt="") so screen readers skip them. Good alt text describes the purpose of the image, not just its appearance.
Examples
Every product photo needs alt text before we publish the page.
The alt text just says 'image1.jpg', which doesn't help anyone.
Usage note
'Alt' here is short for 'alternative'; it has nothing to do with the Turkish word 'alt' (bottom).
Common phrases
write alt text · add alt text · empty alt · descriptive alt text
Software that reads the content of a screen aloud or sends it to a braille display, used mainly by blind and visually impaired people.
Where you use it
Well-known screen readers are NVDA and JAWS on Windows, VoiceOver on Apple devices and TalkBack on Android. Developers test pages with a screen reader and check what it 'announces' for each element.
Examples
The screen reader just says 'button' because the icon button has no label.
Test the checkout with a screen reader such as VoiceOver before the release.
Common phrases
screen reader user · test with a screen reader · screen reader announces · screen-reader-only text
Accessible Rich Internet Applications: a set of HTML attributes, such as role and aria-label, that give assistive technology extra information about elements.
Where you use it
Pronounced like the music word 'aria'. ARIA is used for custom widgets such as tabs, menus and dialogs. A well-known principle says a native HTML element is better than a div with ARIA added to it.
Examples
The icon button needs an aria-label so that screen readers can announce it.
Too much ARIA can make a page harder to use, not easier.
Common phrases
ARIA attributes · aria-label · ARIA role · aria-hidden · ARIA live region
Using a site with the keyboard only, moving between links, buttons and fields with Tab and activating them with Enter or Space.
Where you use it
Developers test keyboard navigation by putting the mouse aside. Key ideas are a visible focus indicator, a logical tab order, no keyboard traps and 'skip to content' links.
Examples
Keyboard navigation breaks in the modal: Tab moves focus to the page behind it.
Someone removed the focus outline, so keyboard navigation is almost impossible now.
Common phrases
keyboard accessible · tab order · focus indicator · keyboard trap · skip link
A number that compares the brightness of text with the brightness of its background; high ratios such as 7:1 are easier to read than low ones such as 2:1.
Where you use it
WCAG level AA asks for at least 4.5:1 for normal text and 3:1 for large text. Designers and developers check colors with contrast checkers or in the browser's developer tools.
Examples
The light grey text on white has a contrast ratio of only 2.8:1.
We darkened the brand blue to reach a 4.5:1 contrast ratio.
Common phrases
color contrast · meet the contrast ratio · low contrast · contrast checker
Search Engine Optimization: work that helps a site's pages to be found, understood and shown higher in search engines such as Google.
Where you use it
Said letter by letter. For developers, technical SEO means clean URLs, fast pages, correct HTML, meta tags, sitemaps and pages that crawlers can render. Marketing teams usually own content and keywords.
Examples
The new site looks great, but we lost traffic because nobody checked the SEO.
Server-side rendering helped our SEO, since search bots now get the full HTML.
Common phrases
technical SEO · SEO-friendly URLs · improve SEO · SEO audit
An HTML tag in the head of a page that gives browsers and search engines information about the page, such as its description or viewport settings.
Where you use it
Common ones are the meta description, the viewport tag, the robots tag and Open Graph tags (og:title, og:image) for link previews on social media. The title tag is often discussed with them but is a separate element.
Examples
Every product page needs its own description meta tag.
The link preview shows no image because the og:image meta tag is missing.
Usage note
Google does not use the old 'keywords' meta tag for ranking.
Common phrases
meta description · robots meta tag · Open Graph tags · add a meta tag
A file, usually sitemap.xml, that lists the pages of a website so that search engines can find and crawl them more easily.
Where you use it
Developers generate sitemaps automatically, list them in robots.txt and submit them in tools such as Google Search Console. Large sites split them into several files with a sitemap index.
Examples
The new blog posts aren't in the sitemap, so Google takes longer to find them.
Regenerate the sitemap every time we publish a product.
Common phrases
XML sitemap · submit a sitemap · sitemap index · generate a sitemap
For a search engine bot to visit pages automatically, follow their links and download their content so that they can be indexed.
Where you use it
The bot is called a crawler or spider; Google's is Googlebot. Developers control crawling with robots.txt and talk about crawl errors and, on very large sites, the 'crawl budget'.
Examples
Googlebot crawled the staging site because nobody had blocked it.
Pages that can only be reached through a search form are hard for bots to crawl.
Usage note
In Turkish, 'tarayıcı' can mean both browser and crawler. In English they are different words: a browser is a program for people, a crawler is a bot.
Common phrases
crawl a site · search engine crawler · crawl budget · crawl errors · block crawlers
For a search engine to store and organize a page after crawling it, so that the page can appear in search results.
Where you use it
People ask 'Is the page indexed?' and use a noindex meta tag to keep pages such as admin screens or thank-you pages out of the results. In databases, an index is something different: a structure that speeds up queries.
Examples
Only half of our product pages are indexed by Google.
Add noindex to the internal search pages so they don't get indexed.
Common phrases
get indexed · noindex · indexed pages · request indexing
The process of checking who a user is, for example with a password, a one-time code or a login through a Google or Apple account.
Where you use it
Often shortened to auth. Teams add, implement or outsource authentication, and talk about two-factor authentication (2FA), single sign-on (SSO), tokens and OAuth.
Examples
Authentication works, but every user can still see the admin page.
We added two-factor authentication to the admin panel.
Usage note
Authentication checks who you are; authorization checks what you are allowed to do. Both are often shortened to 'auth', which can be confusing.
The secure version of HTTP, which encrypts the connection between the browser and the server with TLS so that others cannot read or change the data.
Where you use it
Needs a valid certificate on the server. Browsers mark plain HTTP pages as 'Not secure', and many modern features, such as service workers and geolocation, only work over HTTPS.
Examples
Redirect all traffic from HTTP to HTTPS.
The camera doesn't work on the test site because it isn't served over HTTPS.
Common phrases
over HTTPS · force HTTPS · redirect to HTTPS · HTTPS connection
An attack in which someone gets harmful JavaScript into a page that other users open, for example through a comment, so that the script runs in their browsers.
Where you use it
Usually called XSS. It can be used to steal session data or change what users see. Common defenses are escaping user input, avoiding raw innerHTML and setting a Content Security Policy (CSP) header.
Examples
The search page was open to cross-site scripting because it printed the query without escaping it.
The security report lists two cross-site scripting issues in the comment form.
An attack in which someone types SQL code into a form or URL so that the database runs it, which can expose or delete data.
Where you use it
Happens when user input is pasted directly into a query string. It is prevented with parameterized queries (prepared statements) or an ORM. SQL is said letter by letter or as 'sequel'.
Examples
This login form is vulnerable to SQL injection because it builds the query by joining strings.
Parameterized queries protect us from SQL injection.
Cross-Origin Resource Sharing: browser rules that let a server say which other websites (origins) may read its responses through JavaScript.
Where you use it
Pronounced as one word, 'cors'. The famous 'blocked by CORS policy' error appears when a front end calls an API on another domain that doesn't send the right Access-Control-Allow-Origin header. It is fixed on the server, not in the browser.
Examples
The API works in Postman but fails in the browser with a CORS error.
Ask the back-end team to allow our domain in the CORS settings.
Usage note
CORS does not protect the server; it relaxes the browser's same-origin policy in a controlled way.
Common phrases
CORS error · CORS policy · enable CORS · CORS headers · cross-origin request
Cross-Site Request Forgery: an attack that tricks a logged-in user's browser into sending an unwanted request, such as changing an email address, to a site the user trusts.
Where you use it
Often said as 'sea-surf' or letter by letter. Common protections are CSRF tokens in forms and SameSite cookies, and many back-end frameworks include CSRF protection by default.
Examples
The form fails with 'CSRF token mismatch' because the page was open for too long.
To turn data such as a password into a fixed-length string with a one-way function, so that the original value cannot be read back from it.
Where you use it
Passwords are hashed with slow algorithms designed for the job, such as bcrypt or Argon2, together with a random salt. The noun is also hash: at login, the system hashes the typed password and compares the two hashes.
Examples
We never store passwords in plain text; we hash them with bcrypt.
The old system hashed passwords with MD5, which is no longer considered safe.
Usage note
Hashing is not encryption: encrypted data can be decrypted with a key, but a hash cannot be reversed.
Common phrases
hash a password · password hash · hashing algorithm · salt and hash
Ten questions from this glossary. Pick the right meaning for each term and see your score.
How to learn web development vocabulary
Read real texts from the field every day: MDN Web Docs, the official documentation of the framework you use, release notes and the discussions in GitHub issues.
Keep your browser's developer tools and your code editor in English, so the console errors and warnings you see match the words you will search for.
Notice that many code words are ordinary English words: margin, padding, fetch, render and deploy all have everyday meanings, and knowing them makes the technical meaning easier to remember.
Learn terms together with their partners: not just 'cache' but 'clear the cache', 'cache headers' and 'it's a cache issue'.
Say abbreviations out loud the way developers do: HTML, CSS and URL letter by letter, JSON like the name Jason, and DOM, CORS and REST as single words.
Frequently asked questions
How can I learn English vocabulary for web development?
Read real texts from the field and notice how words are used: MDN Web Docs, framework guides, changelogs, browser error messages and GitHub issue threads. Learn each term with its common partners (clear the cache, deploy to staging) and use new words right away in your commit messages, tickets and code comments.
Which web development terms should I learn first?
Start with the words you meet on day one: browser, server, HTML, CSS, JavaScript, element, selector, request, response, API, front end, back end and deploy. Then add layout and framework vocabulary, and after that performance, accessibility, SEO and security terms. This glossary is ordered the same way, from most to least essential.
How do developers pronounce HTML, JSON, SQL and other web abbreviations?
Most are said letter by letter: HTML, CSS, URL, API, DNS and CDN. Some are read as words: JSON sounds like the name Jason, and DOM, CORS, REST and ARIA are said as single words. SQL can be letter by letter or 'sequel'. Two common traps: cache sounds like 'cash', and Nginx is 'engine x'.
Is it front end, front-end or frontend?
All three are used. Traditional style writes the noun as two words (work on the front end) and adds a hyphen before another noun (a front-end developer). Many tech companies simply write frontend and backend as one word. Any choice is fine as long as you use it consistently in the same text.
Should I use the Turkish or the English term at work?
Turkish web teams keep many English words, such as frontend, deploy, cache, component and state, often with Turkish endings ('deploy etmek', 'cache'i temizlemek'). Words like tarayıcı, sunucu, alan adı and erişilebilirlik are just as common in speech and in formal documents. Knowing both lets you move easily between a Turkish meeting and English documentation.
