Website glossary.
Make sense of it.

A set of HTML attributes (role, aria-*) describing the role, state and name of UI elements for assistive technologies such as screen readers.

aria-label gives an element an accessible name that screen readers announce. Use it when an element has no visible text, such as an icon-only button.

rel="canonical" tells search engines which duplicate URL is the primary one. When it is the right tool, when a 301 redirect is, and why Google can ignore it.

HTTP header declaring allowed sources for scripts, styles and other resources. One defence layer that limits the impact of some XSS attacks.

Contrast ratio ranges from 1:1 to 21:1. Check WCAG 2.2 thresholds: 4.5:1 for normal text, 3:1 for large text and interface elements.

A set of three Google metrics (LCP, INP, CLS) measuring loading speed, interaction responsiveness and visual stability of a page under real-world conditions.

The number of URLs a search engine bot can and wants to crawl on a site within a given time. Critical for large and frequently changing websites.

CLS measures visual stability: the largest sum of unexpected layout shifts within a session window. A good p75 score is ≤ 0.1.

FCP is the time from navigation start until any page content is rendered. A good FCP is 1.8 s or less; over 3 s is poor.

Hreflang tells search engines which language version suits which audience. See self referencing hreflang, return tags and when to use x-default.

An HTTP header forcing the browser to connect to a site exclusively over HTTPS for a declared period. Protects against SSL stripping attacks.

Removing unnecessary characters and comments from text assets to reduce their size without changing how the code runs.

A Core Web Vitals metric measuring the latency between a user interaction (click, tap, key press) and the next screen paint. A good score is ≤ 200 ms.

Transforming JavaScript to make quick reading harder without hiding it from a browser user; learn its limits, risks and safer ways to protect secrets.

The html lang attribute declares a document language and shapes screen reader pronunciation. See how it differs from hreflang and meta content-language.

A Core Web Vitals metric measuring the time from page load start until the largest content element is rendered. A good score is ≤ 2.5 s.

An industry term for the value of signals conveyed through links. Useful for discussing internal linking, but not a publicly measurable Google score.

A directive telling search bots not to add a page to the index. It does not block crawling. It disables indexing via meta robots or X-Robots-Tag.

Measuring performance and errors from data collected from a site's real users: in their browsers, on their networks and devices.

A soft 404 is a page that says the content does not exist, or is empty, while returning 200. Google does not index it and flags it in Search Console.

A standard format for describing page content, usually JSON-LD with Schema.org, that helps search engines understand a page and qualify it for rich results.

Time until the first response byte. Navigation TTFB also includes connection setup and network delay; a good guideline is ≤ 800 ms.

A title tag is the <title> element search engines use to build a result title link. See how it differs from an H1 and why Google rewrites titles.

TBT adds up the time long tasks block the main thread after FCP. It is a Lighthouse lab metric; a good mobile result is 200 ms or less.

Uptime is availability, an SLO is a target, and an SLA sets contractual commitments. A 99.9% time-based target allows 43 min 12 s downtime over 30 days.

The viewport meta tag tells mobile browsers how wide the page layout should be. Without it, phones render the page at desktop width and shrink it.

The W3C international standard for web content accessibility. It defines success criteria at levels A, AA and AAA; the current version is WCAG 2.2.

The CO₂e emissions generated by a website: data transfer, data centers, networks and user devices. Estimated with models such as Sustainable Web Design v4.

A compact web font format, usually smaller than TTF and OTF because it uses Brotli compression; learn when conversion improves web delivery.

An XML file listing a site's URLs with metadata (lastmod) that helps search engines discover and refresh pages. Defined by the sitemaps.org standard.