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

Conversion rate is the ratio of visits or interactions in which the desired action on a site (quote form, sample request, purchase) is completed to all visits or interactions. Certified manufacturing

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

D

Digital product passport A digital product passport is the record that electronically links to a product the product information to be specified separately for each product group under the EU’s Ecodesign Regulation (ESPR). Certified manufacturing

E

EN 301 549 (Accessibility requirements for ICT products and services) is the European standard, published jointly by CEN, CENELEC and ETSI, that defines the accessibility requirements for information and communication technology products and services and how they are to be tested. Accessibility

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

EU declaration of conformity An EU declaration of conformity is the document, drawn up and signed by the manufacturer or its authorized representative, in which the manufacturer declares under its own responsibility that a product meets the requirements of the EU legislation that applies to it. Certified manufacturing

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

Global ACI (Global Accreditation Cooperation Inc.) is the organization that runs the international mutual recognition arrangement of accreditation bodies and replaced IAF, which ceased operations on January 1, 2026. Certified manufacturing

H

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

I

Index (search index) The index is the database in which a search engine keeps the pages it has decided to store out of those it crawled, and the only place it selects search results from; it is also called the search index. Being found on Google

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

ISO/IEC 17025 is the international standard that sets the requirements for the competence, impartiality and consistent operation of testing and calibration laboratories, and on which laboratory accreditation is based. Certified manufacturing

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

M

Mobile-first indexing means that Google bases indexing and ranking of a page on the version of the page shown to its smartphone crawler. Certified manufacturing

N

noindex is a directive asking that a page not be added to a search engine’s index, given either with the robots meta tag inside the page or with the server’s X-Robots-Tag response header. Being found on Google

R

Redirect chain A redirect chain is when an address reaches its final address not in a single hop but by passing through more than one redirect; for example, if an old address is redirected first to an intermediate address and from there to the final address, there is a two-hop chain. Site migration

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

Search Console is a free service from Google for monitoring a site’s status in Google Search and for seeing and fixing its problems. Being found on Google

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

Sitemap A sitemap is a file, usually written in XML, that lists the addresses of a site’s pages and, optionally, their last modification dates for search engines in a single file. Being found on Google

Social compliance audit A social compliance audit is the examination by an independent auditor of working conditions, occupational health and safety and business ethics at a production site against a code of conduct. Certified manufacturing

Soft 404 A soft 404 is a page that shows visitors “page not found” or empty content but returns a 200 (success) code from the server instead of an error code; Google treats these pages as error pages and does not index them. Site migration

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

TLS certificate lifetime is the period from the day the certificate that provides a site’s HTTPS connection is issued to the day its validity ends. Certified manufacturing

Total cost of ownership is the sum of all the costs of buying an asset or service and using it over its service life. Certified manufacturing

Transaction certificate A transaction certificate is the document, issued by a certification body under Textile Exchange standards, that shows a specific delivered consignment of goods is certified. Certified manufacturing

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

U

URL inventory A URL inventory is a single list that gathers every address of a site that search engines know — current pages, address variants and old addresses; in a site redesign or migration, the redirect map is derived from this list. Site migration

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