Web development glossary: 40 terms in one sentence each

The short answer

Proposals, previews and progress updates about a website use a vocabulary that is rarely explained, and a business owner who knows forty terms can follow almost any conversation about their site and ask the right questions. The terms below fall into five groups: how a site is built, how it is styled and structured, how it performs, how it is measured, and how it is shipped. Each is explained in one plain sentence. When a term is used to justify a choice or a price, ask what it changes for your site and what the alternative would have been; the answer is usually shorter than the word suggested.

How a site is built

Term	In one sentence
HTML	The markup that defines a page’s content and structure: headings, paragraphs, links, images, forms.
CSS	The styling language that defines how HTML looks: colours, type, spacing, layout, on every screen size.
JavaScript	The programming language that runs in the browser to add behaviour, and the main reason pages feel slow when overused.
TypeScript	JavaScript with types, which catches a class of mistakes before the code runs and is why we write in it.
Framework	A set of tools and conventions for building a site or application, such as Astro for websites and Next.js for applications.
Static site	A website delivered as ready-made files, built in advance, with no server computing pages per visit.
Server rendering	Building a page on a server at the moment it is requested, needed for personalised or constantly changing content.
Islands	Small interactive components loaded into an otherwise static page, so JavaScript runs only where it is needed.
Component	A reusable piece of interface, such as a button or a card, built once with its behaviour and styling and used everywhere.
Component library	The collection of a site’s components, styled from its tokens and documented, from which pages are assembled.
Design system	The tokens, components, patterns and principles that make a site consistent and refreshable in place.
Design tokens	Named values for colours, type and spacing that every component uses, so a change in one place changes the whole site.
Headless CMS	A content system that stores and edits content and hands it to the site through an API, without rendering pages itself.
Content model	The definition of what a piece of content consists of, such as an article’s title, summary, body, image and topics.
Markdown	A plain-text way of writing formatted content that is easy to edit, version and build into pages.

How a site is structured and styled

Term	In one sentence
Semantic HTML	Using the elements that describe meaning, such as headings, lists and navigation, so browsers, search engines and assistive technology understand the page.
Responsive design	Layout that adapts to the screen size, from phone to large monitor, from one set of code.
Mobile first	Designing and building for the phone first and expanding for larger screens, rather than shrinking a desktop design.
Progressive enhancement	Building the essentials to work with HTML and CSS and adding JavaScript as improvement, so the site works when scripts fail.
Accessibility	Building so that people with disabilities can use the site, measured against the WCAG standard and required by law for many organisations.
WCAG	The Web Content Accessibility Guidelines, the international standard, with level AA as the usual legal and contractual target.
Structured data	Machine-readable annotations describing a page’s content, such as a business, an article or a product, used by search engines and assistants.
Canonical URL	The address declared as the main one for a page’s content, so duplicates do not compete with each other in search.

How a site performs

Term	In one sentence
Core Web Vitals	Three measurements of loading, responsiveness and visual stability that search engines use to judge page experience.
Largest Contentful Paint	How long until the main content of a page is visible, the loading measurement.
Interaction to Next Paint	How quickly the page responds when a visitor taps or clicks, the responsiveness measurement.
Cumulative Layout Shift	How much the layout moves unexpectedly while loading, the visual stability measurement.
Lab data	Measurements from a tool loading a page under simulated conditions, useful for diagnosis.
Field data	Measurements from real visitors’ browsers, which is what search engines use and what visitors experienced.
Performance budget	Limits on page weight and metrics, enforced in the pipeline so a site cannot slowly get heavier.
Lazy loading	Loading images and components only when they are about to be seen, so the first view is light.
Third-party script	Code from another company running on your page, such as analytics or a chat widget, each a cost in speed and privacy.

How a site is shipped

Term	In one sentence
Repository	The versioned store of the site’s code, content and setup, which the business must own.
Version control	The system that records every change, who made it and why, and lets any change be undone.
Build	The step that turns source code and content into the files visitors receive.
Pipeline	The automated sequence of checks, build and deployment that every change passes through.
Preview	A copy of the site built from a proposed change, at its own address, so it can be reviewed before it goes live.
Deployment	Putting a built version of the site live, atomically, with the previous version kept for rollback.
Rollback	Restoring the previous version in one step when a change turns out wrong.
Technical debt	The accumulated cost of shortcuts, which shows up as a slower site and slower changes until it is paid down.

Using the glossary

What this means for you

Forty terms cover almost every conversation about building, styling, measuring and shipping a website. Knowing them lets you read a proposal for what it buys, a progress update for what happened, and a hand-over for what you own. Ask about anything that does not fit, and treat words that cannot be explained plainly as a reason to ask more, not as a reason to pay more.