Web Development glossary

105 Web Development terms, from Novice to Master. Start with the basics or jump to a level.

Updated October 16, 2026

Novice

Absolute Path: An absolute path is the entire path of a resource.
API: A set of rules that lets one program ask another for data or actions.
Browser default styles: Styles the browser adds before yours, like blue links and heading sizes.
Client and Server: The client asks; the server answers.
Color: The color property sets text color; colors can be names, hex or rgb().
External stylesheet: A separate .css file that pages load with a <link> tag.
Fragment identifier: The portion of a URL that appears after the # symbol.
HTTP: The request-and-response language of the web.
HTTPS: HTTP over an encrypted connection.
Inline style: CSS written on one element with the style attribute.
Internal stylesheet: CSS inside a <style> tag that styles only that page.
JSON: The text format most APIs use for data.
Kebab Case: All letters are lower case. Each word is separated by an dash.
Link element: This loads an external stylesheet.
Pixel: px: a fixed unit of size on screen.
Relative Path: A relative path is where the path of a resource is defined in relation to the current…
Request: What the client sends: method, URL, headers and an optional body.
Response: What the server sends back: a status code, headers and usually a body.
URL: The full address of a resource on the web.
Web API: An API you call over HTTP, usually getting JSON back.

Apprentice

200 OK: The request worked and the body holds the result.
201 Created: A new resource was created.
204 No Content: It worked and there is no body to return.
400 Bad Request: The request is invalid, such as a missing or wrong field.
401 Unauthorized: No valid credentials were sent: sign in first.
403 Forbidden: Signed in, but not allowed to do this.
404 Not Found: Nothing exists at that URL.
500 Internal Server Error: Something broke on the server.
Content-Type: The header that says what format a body is in.
DELETE (HTTP): The method that removes a resource.
GET: The method that reads data without changing anything.
Header: A name-value line of extra information on a request or response.
HTTP Method: The verb that says what a request wants to do.
PATCH: The method that updates only some fields of a resource.
POST: The method that creates a new resource.
POST form submission: A form submission that sends form data in the request body.
PUT: The method that replaces a whole resource.
Query String: The ?key=value part of a URL, used for filters and paging.
Request Body: The data sent with a request, usually JSON.
Status Code: The three-digit result number: 2xx success, 4xx client error, 5xx server error.
Viewport: The visible area of the page; vw and vh measure it.

Journeyman

409 Conflict: The request clashes with the current state, like a duplicate.
422 Unprocessable Content: Well-formed data whose values break the rules.
429 Too Many Requests: You sent too many requests; wait and try again.
aria-hidden: An ARIA attribute that removes an element and its descendants from the accessibility tree when true.
aria-label: An ARIA attribute that supplies an accessible name as a text value.
aria-labelledby: An ARIA attribute that uses other elements' text to form an accessible name.
Art direction: Providing differently composed or cropped images for different presentation conditions.
Authentication: Proving who you are.
Authorization: Deciding what an identified user is allowed to do.
Breakpoint: A screen width where the layout changes.
Canonical link: A link identifying the preferred URL for content available through multiple URLs.
Character encoding declaration: Markup near the start of a document that declares its text encoding as UTF-8.
Cookie: Small data the browser stores and sends back to the same site on every request.
CORS: Server rules that tell browsers which other sites may call it.
Document language: The primary human language of a document or element's text.
Favicon: An icon associated with a website or page for browser tabs, bookmarks, and similar interfaces.
JWT: A signed token carrying who the user is and when it expires.
Lazy loading: Delaying an off-screen resource until it is likely to be needed.
Location Header: A header pointing to a new resource or a redirect target.
Media query: Applies CSS only when a condition is true, like a minimum screen width.
Meta description: A short document summary supplied as metadata, often used by search and sharing tools.
Mobile-first design: Phone layout first, then media queries for bigger screens.
noopener: A link relationship that prevents a newly opened page from receiving an opener reference.
noreferrer: A link relationship that omits referrer information and also prevents an opener relationship.
prefers-color-scheme: Checks whether the user prefers a light or dark theme.
prefers-reduced-motion: Checks whether the user asked for less animation.
Responsive design: One page that adapts its layout to any screen size.
Responsive image: An image setup that lets the browser select a suitable resource for the display and layout.
Safe Method: A method that only reads and never changes data, like GET.
tabindex: A global attribute that controls whether and where an element participates in sequential focus navigation.
Text direction: The direction in which text and inline content progress.
Viewport metadata: Metadata that guides how a page's viewport is sized and scaled on mobile devices.

Freelancer

Caching Headers: Headers that say how long a response may be reused.
Conditional Request: A request that only proceeds if the resource is still in the expected state.
Content Negotiation: The client asks for a format with Accept; the server picks one it supports.
crossorigin: An attribute that configures a cross-origin request and whether credentials are included.
ETag: A version fingerprint that lets clients skip downloading unchanged data.
Focusable area: A page region or control that can become the target of keyboard focus.
Iframe sandbox: Restrictions applied to content in an iframe through its sandbox attribute.
Light dismiss: Closing a temporary interface by interacting outside it or making a platform close request.
Multipart form data: A form encoding that separates entries into parts and supports file uploads.
nonce attribute: A one-use token that a Content Security Policy can require on allowed inline script or style elements.
OAuth 2.0: A standard for granting apps limited access via tokens instead of passwords.
OpenID Connect: Sign-in built on OAuth 2.0; used by "Sign in with Google".
Preflight Request: The OPTIONS check a browser sends before some cross-origin requests.
referrerpolicy: An attribute that controls which referrer information is sent when fetching or navigating.
Refresh Token: A long-lived token used to get new short-lived access tokens.
Sequential focus navigation: Moving focus through eligible page controls in an ordered sequence, commonly with the Tab key.
Subresource integrity: A security feature that checks a fetched resource against an expected cryptographic hash.
URL-encoded form data: A form encoding that represents name-and-value pairs using URL-style escaping.

Master

Compositing: Combining painted layers into the final picture.
Critical CSS: The styles needed for the first screen, inlined so it shows fast.
CSS Object Model: The browser's in-memory model of the page's CSS, readable from JavaScript.
HTML parser: The browser component that turns HTML source into a document tree.
HTTP/2 and HTTP/3: Newer HTTP versions that send many requests at once over one connection.
Layout: The step where the browser works out every box's size and position.
MathML namespace: The namespace URI that identifies inline MathML elements in a document tree.
Mutual TLS: Both client and server present certificates to prove who they are.
Reflow: The browser redoing layout after a size or position change.
Repaint: Redrawing pixels after a look changes, without a size change.
Server-Sent Events: A response kept open so the server can push a stream of events.
Style invalidation: Working out which elements need styles recalculated after a change.
SVG namespace: The namespace URI that identifies inline SVG elements in a document tree.
text/html MIME type: The media type that identifies a resource as an HTML document parsed with HTML syntax.

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