Glossary.

A

Accessibility tree The accessibility tree is the structure a browser derives from a page and presents to assistive technology; it is the page a screen reader sees. Accessibility

Accessible name The accessible name is the name of an interface element as read by assistive technology, and it can differ from the text shown on screen. Accessibility

AEO (Answer Engine Optimization) is the practice of getting content selected as the unit that answers a question directly. Answer engines

AI Overviews is the AI-generated summary Google shows above the search results page, synthesised from more than one source. Answer engines

ARIA (Accessible Rich Internet Applications) is a set of attributes used to convey role, state and property information to assistive technology where HTML cannot express it on its own. Accessibility

B

Brand mention A brand mention is a brand’s name being named without a link, and in the era of answer engines it is a visibility signal independent of links. Answer engines

C

Cache header A cache header is the server response header that tells the browser how long a resource may be stored and how it is to be revalidated. Performance

Canonical address A canonical address is the markup declaring which page is the original when the same or very similar content is reachable from more than one address. Multilingual

Citation A citation is an answer engine mentioning a source in the answer it produces, usually with a link to it. Answer engines

CLS (Cumulative Layout Shift) measures how much content shifts unexpectedly while a page is loading or in use, and Google counts anything under 0.1 as good. Performance

Colour blindness is the inability to tell certain colours apart, and it affects a considerable share of the world’s population, men in particular. Accessibility

Compression is the shrinking of text-based resources before they are sent from the server and their expansion in the browser. Performance

Core Web Vitals is the collective name for the three metrics Google defined to measure a page’s real user experience. Performance

Country domain (ccTLD) A country domain is a two-letter top-level domain extension allocated to a particular country. Multilingual

Crawl budget is the number of requests a search engine allocates to fetching from a site within a given period. Answer engines

Critical rendering path The critical rendering path is the minimum sequence of steps a browser must complete before it can draw a page on screen. Performance

E

Entity An entity means a distinct thing that search and answer engines recognise — a person, an organisation, a place, a product or a concept. Answer engines

F

Field data is the sum of performance measurements experienced by real users on real devices and real networks. Performance

Focus trap A focus trap is when keyboard focus enters a region and cannot leave it again, and WCAG prohibits it explicitly at level A. Accessibility

Font subset A font subset is a font file regenerated with only the characters that are needed. Multilingual

G

GEO (Generative Engine Optimization) is the work of increasing the likelihood that a site is chosen as a source in the answers generated by AI systems. Answer engines

H

hreflang is the markup that declares a page’s different language and region versions to search engines. Multilingual

I

IndexNow is an open protocol that tells search engines immediately that a page has changed. Answer engines

INP (Interaction to Next Paint) is the time from a user interaction until the page responds visually, and Google counts anything under 200 milliseconds as good. Performance

J

JSON-LD (JavaScript Object Notation for Linked Data) is a structured data format that declares a page’s meaning in a machine-readable form without changing the page’s appearance at all. Answer engines

L

Language tag (BCP 47) A language tag is the standard coding form that tells machines which language a text is in. Multilingual

LCP (Largest Contentful Paint) is the paint time of the largest content element in a page’s visible area, and Google counts anything under 2.5 seconds as good. Performance

Live region A live region is an area of a page whose changes a screen reader has to announce to the user. Accessibility

llms.txt is an optional file placed in a website’s root directory that summarises, in Markdown, what the site is about and where its most important pages are for language models. Answer engines

Locale A locale is the setting that defines a user’s language and region together and determines the formatting rules. Multilingual

Localisation (Localization) is adapting content to the culture, habits and search language of a target market; it is a wider undertaking than translation. Multilingual

R

Reflow A reflow is the browser recomputing the positions and sizes of elements on a page after a change. Performance

Relative luminance is the value expressing a colour’s perceived lightness between 0 and 1, and it is the basis of the contrast ratio calculation. Accessibility

S

Screen reader A screen reader is assistive technology that turns on-screen content into speech or braille output and lets the user navigate by keyboard. Accessibility

Semantic HTML means choosing each element for its meaning rather than its appearance — a heading element for a heading, a button element for a button, a list element for a list. Accessibility

Structured data is an additional layer that labels a page’s content with a standard vocabulary machines can understand. Answer engines

T

Text expansion is the same content being of different lengths in different languages, and the layout having to flex accordingly. Multilingual

Translation memory A translation memory is a database that stores previously translated sentences and suggests them when the same or a similar sentence comes up again. Multilingual

TTFB (Time to First Byte) is the time between the browser sending a request and receiving the first byte from the server. Performance

W

WCAG (Web Content Accessibility Guidelines) is the international standard published by the W3C that defines the accessibility of web content through testable success criteria. Accessibility

X

x-default is a special hreflang value declaring the default page to show when no language version matches the user’s language. Multilingual