Glossary
Plain definitions of the terms used in our reports and guides.
- Accessibility overlay
A script added on top of a website that claims to fix accessibility automatically. It doesn’t change the site’s own code; in 2025 the FTC ordered one vendor, accessiBe, to pay $1 million over its claims.
Accessibility Fix ReportFTC, April 2025 (opens in a new tab)
- ADA Title III
The part of the Americans with Disabilities Act that covers public accommodations. US courts and the Department of Justice have applied it to many business websites, which is the basis of most website demand letters.
Accessibility Fix ReportADA.gov web guidance (opens in a new tab)
- Alt text
A text alternative for an image, written in the alt attribute. Screen readers read it aloud; decorative images use an empty alt so they are skipped (WCAG 1.1.1).
Accessibility Fix ReportW3C images tutorial (opens in a new tab)
- ARIA
Accessible Rich Internet Applications: attributes such as aria-label and role that give assistive technology information HTML alone doesn’t. Native HTML elements are preferred where they exist.
Accessibility Fix ReportW3C WAI-ARIA overview (opens in a new tab)
- Canonical URL
The preferred address of a page that exists at several URLs, declared with a link rel="canonical" tag, so search engines consolidate them.
- Chrome UX Report (CrUX)
Google’s public dataset of real Chrome users’ experience, including Core Web Vitals at the 75th percentile. Sites need enough traffic to appear.
- Colour contrast ratio
How different text is from its background, from 1:1 to 21:1. WCAG 1.4.3 asks for at least 4.5:1 for normal text and 3:1 for large text.
Accessibility Fix ReportUnderstanding SC 1.4.3 (opens in a new tab)
- Content Security Policy (CSP)
A response header that limits where scripts, styles and frames may load from, reducing the impact of injected code.
- Cumulative Layout Shift (CLS)
How much content moves unexpectedly while a page loads. Good is 0.1 or less.
- DKIM
DomainKeys Identified Mail: a signature added to each email, checked against a public key published in DNS under a selector.
- DMARC
A DNS policy telling inboxes what to do with mail that fails SPF and DKIM alignment (none, quarantine or reject) and where to send reports.
- EN 301 549
The European standard for accessibility of ICT products and services. Its clause 9 covers web content and incorporates the WCAG success criteria.
- European Accessibility Act (EAA)
EU Directive 2019/882. Since 28 June 2025 it requires many products and services, including e-commerce services for consumers, to meet accessibility requirements, with an exemption for micro-enterprises providing services.
EAA Readiness ReportEUR-Lex, Directive (EU) 2019/882 (opens in a new tab)
- HSTS
HTTP Strict Transport Security: a response header telling browsers to always use HTTPS for your site.
- Interaction to Next Paint (INP)
How quickly a page responds to taps, clicks and key presses, across the visit. Good is 200 ms or less. It replaced First Input Delay as a Core Web Vital in March 2024.
- Keyboard trap
A place where keyboard focus gets stuck and Tab can’t move on, such as a modal or cookie banner. WCAG 2.1.2 forbids it.
Accessibility Fix ReportUnderstanding SC 2.1.2 (opens in a new tab)
- Largest Contentful Paint (LCP)
How long the largest image or text block takes to appear. Good is 2.5 seconds or less at the 75th percentile of visits.
- Mixed content
Files loaded over plain HTTP on an HTTPS page. Browsers block or warn about them.
- noindex
A robots meta tag or header telling search engines not to show a page in results.
- Open Graph tags
Meta tags such as og:title and og:image that control how a link looks when shared on social networks and messaging apps.
- Screen reader
Software that reads a page aloud or to a braille display, such as VoiceOver, NVDA or JAWS. It relies on names, labels and structure in the code.
- security.txt
A file at /.well-known/security.txt that tells security researchers how to report a problem to you.
- SPF
Sender Policy Framework: a DNS TXT record listing the servers allowed to send email for your domain. A record may trigger at most 10 DNS lookups.
- Structured data
Machine-readable facts about a page, usually JSON-LD using schema.org types such as Product, which search engines can show as rich results.
- Success criterion
One testable requirement in WCAG, numbered like 1.4.3 (Contrast, minimum). Reports cite the criterion each failure breaks.
- Total Blocking Time (TBT)
In a lab test, the time scripts keep the page from responding between first paint and interactivity. It tracks the problems INP measures in the field.
- WCAG
The Web Content Accessibility Guidelines, published by the W3C. Version 2.2 (December 2024) has success criteria at three levels, A, AA and AAA; laws and settlements usually point to level AA.
- XML sitemap
A file that lists the pages you want search engines to find, usually at /sitemap.xml.