Glossary
Terms used in accessibility research and practice. Each entry has a definition, common aliases, and category tags.
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- Failure Mode(also: Accessibility failure mode)
- In accessibility evaluation, any hindrance caused by a product or web site that prevents a user with a disability from achieving a goal with the same effectiveness, efficiency or safety as a non-disabled user. The term is borrowed from reliability engineering and is used to…
- Failure Rate(also: FR (accessibility metric))
- An accessibility metric introduced by Sullivan and Matson (2000) that, for a given page and a given checkpoint, divides the number of checkpoint violations found by the maximum number of violations that could have occurred on that page. Failure Rate produces a normalised value…
- Functiona11ity Error(also: Functionality Error, Functiona11ity)
- A term coined by Zhong et al. (2026) — a portmanteau of 'functionality' and 'a11y' (accessibility) — for an accessibility barrier that only manifests through interaction. The static state of the UI appears accessible (elements have labels, sufficient contrast, correct roles),…
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