RESOURCES

The web build glossary.

Last updated: July 2026

26 plain-language definitions spanning web development, frontend performance, accessibility, cloud infrastructure and AI — the terms behind everything we build. In short: this is a plain-language reference to the words that come up when you build a modern website or web application — from architecture choices like headless CMS and static-site generation, to the Core Web Vitals that measure real-world speed, to the WCAG 2.2 AA accessibility standard every build should meet. The 26 terms below are grouped by theme and alphabetised within each group, so you can scan straight to the one you need.

Web development & architecture

API (Application Programming Interface): A defined way for one piece of software to request data or actions from another. On the web, APIs let a site or app pull in content, process payments or connect to third-party services without exposing the systems behind them.
Headless CMS: A content management system that stores and manages content but leaves the presentation to a separate front end, delivering content over an API instead of rendering pages itself. It lets one content source feed a website, an app and other channels at once — platforms like Sanity, Contentful and Strapi work this way.
Hydration: The process of attaching JavaScript behaviour to HTML that was already rendered on the server, so an interactive component 'wakes up' in the browser. Sending less JavaScript to hydrate — or hydrating only the parts that need it — keeps pages fast, which is why static-first frameworks hydrate selectively rather than all at once.
JAMstack: An architecture that serves pre-built markup from a CDN and adds dynamic features through JavaScript and APIs, rather than generating every page on a server at request time. It typically means faster, more secure, more scalable sites — the philosophy behind static-first builds.
Progressive Web App (PWA): A website built to behave like an installed app — it can be added to a home screen, work offline or on poor connections, and send notifications — while still being a normal, linkable web page underneath.
Server-Side Rendering (SSR): Generating a page's HTML on the server for each request, so the browser receives fully-formed content immediately. Useful for pages whose content changes per user or per request, at the cost of doing work on every visit.
Static Site Generation (SSG): Building every page to plain HTML ahead of time, at deploy, so visitors are served pre-rendered files straight from a CDN with no per-request server work. It is the fastest, most resilient way to serve content that does not change per user — the default for a static-first build.
Web application: Software delivered through a browser rather than installed on a device — a dashboard, portal or SaaS front end — where the page is an interactive app, not just a document to read.

Frontend performance

Cumulative Layout Shift (CLS): A Core Web Vital measuring how much a page unexpectedly moves around as it loads — for example, when a late-loading image shoves text down. Lower is better; a stable layout means visitors do not lose their place or mis-tap.
Core Web Vitals: Google's set of real-world user-experience metrics — Largest Contentful Paint, Interaction to Next Paint and Cumulative Layout Shift — that measure loading speed, responsiveness and visual stability, and feed into search rankings.
Interaction to Next Paint (INP): A Core Web Vital measuring how quickly a page visibly responds after a user interacts with it — a tap, click or key press. Low INP means the interface feels snappy rather than laggy.
Largest Contentful Paint (LCP): A Core Web Vital measuring how long the largest visible element — usually a hero image or headline — takes to render, as a proxy for how quickly a page feels loaded. A static-first build commonly reaches a sub-1-second LCP at launch.
Lighthouse: Google's open-source auditing tool that scores a page from 0 to 100 on performance, accessibility, best practices and SEO. It is a useful, repeatable benchmark — every Wave18 build targets a 95+ performance score across every page.
Time to First Byte (TTFB): The time between a browser requesting a page and receiving the first byte of the response. Serving pre-built pages from a CDN close to the visitor keeps TTFB low, which in turn helps every metric that follows it.

Accessibility & standards

ARIA (Accessible Rich Internet Applications): A set of HTML attributes that describe the role, state and properties of interactive elements to assistive technology when native HTML alone is not enough — for example, telling a screen reader whether a custom accordion is expanded or collapsed. Correct semantic HTML first, ARIA only where it adds what HTML cannot.
Alt text: A short written description of an image, read aloud by screen readers and shown if the image fails to load. Meaningful images need descriptive alt text; purely decorative ones are marked as decorative so assistive technology skips them.
European Accessibility Act (EAA): EU legislation requiring certain digital products and services to meet accessibility requirements, in practice aligned with the EN 301 549 standard and WCAG. It is why building to a recognised accessibility standard from the start — rather than retrofitting — matters for businesses trading in Europe.
Hreflang: An HTML attribute that tells search engines which language and regional version of a page to show a given visitor, so a UK visitor and a German visitor each land on the right localised version. Essential for a multilingual site — Wave18 builds ship hreflang across six languages from day one.
Semantic HTML: Using HTML elements for their real meaning — headings, lists, buttons, navigation landmarks — rather than generic containers styled to look the part. Semantic markup is the foundation of an accessible, machine-readable page, benefiting screen readers and search engines alike.
WCAG 2.2 AA: The Web Content Accessibility Guidelines, version 2.2, at conformance Level AA — the widely accepted benchmark for accessible web content, covering contrast, keyboard operation, focus visibility, resizable text and more. It is the standard Wave18 builds to and tests against, including manual keyboard and screen-reader testing.

Cloud & infrastructure

CDN (Content Delivery Network): A globally distributed network of servers that caches a site's files close to visitors, so pages load from a nearby location rather than a single distant origin. It is what makes a static-first site fast for a UK and an EU visitor alike.
CI/CD (Continuous Integration / Continuous Deployment): An automated pipeline that builds, tests and deploys code changes so releases become a repeatable process measured in minutes, not a risky manual event. It catches problems before they reach production and makes shipping routine.
Edge: Computing that runs at CDN locations physically close to the visitor, rather than in one central data centre — used to serve pages and run lightweight logic with minimal latency, wherever in the world a request comes from.
Infrastructure as Code (IaC): Defining servers, networks and cloud resources in version-controlled configuration files rather than clicking through a console by hand. It makes infrastructure repeatable, reviewable and quick to recreate — the opposite of undocumented, manually-built environments.

AI in web products

LLM (Large Language Model): An AI model trained on large amounts of text to understand and generate language — the technology behind chatbots, content generation and AI assistants. In a web product it is integrated securely through an API, not bolted on as an afterthought.
RAG (Retrieval-Augmented Generation): A technique that grounds an AI model's answers in a specific, trusted source — such as your own documentation or product catalogue — by retrieving relevant passages and feeding them to the model at answer time. It keeps an AI assistant accurate and on-brand rather than relying on the model's general training alone.