Unusual Words
Where a word or phrase is used in an unusual or restricted way, the reader needs a way to find the definition you meant. Idioms and jargon are named in the rule itself. The scope is narrower than the name suggests. It is not every word a newcomer might not know. It is words where the reader has to pick the right sense out of several to follow the sentence, and W3C says authors may assume readers will use context to work the rest out.
Why it matters
Idiom is the case where the individual words tell you nothing. Spilling the beans has no beans in it, and you cannot swap in a synonym without losing the meaning, which is exactly why idiom does not survive translation. Jargon is the case where a field has quietly given an ordinary word a new job. And an invented word gets no exemption for being new, since a word nobody has ever met is the hardest of the three.
Who this rule protects
People with cognitive and learning disabilities who find words hard to decode or to understand. W3C names a third group that surprises people, readers using a screen magnifier, who lose the surrounding context that would otherwise settle the meaning.
How to check it yourself
- Read the page as somebody new to the subject would, and mark the terms where you would have to know which definition applies.
- Leave alone the words the sentence already settles. W3C's example is gig, which means one thing in an article about concerts and another in an article about disk space, and context tells you which.
- Check idiom as well as jargon, and check any word you invented, because new words carry no exemption.
- Where a word carries two different meanings on the same page, check that each occurrence has its own definition. A glossary is not enough in that case.
Failures we see most often
- Specialist terms run through the site with no definition anywhere a reader can reach.
- A product invents a word for a feature and never explains it.
- One term is used two ways on the same page, with a single glossary entry covering only one of them.
Who this one is for
Read from this rule's own note above, so the grouping and the note cannot disagree.
- Low visionpeople who can see the screen but not easily
- Cognitive and learningpeople for whom the difficulty is understanding, remembering, or staying with it
How to fix it
- Gloss a term in passing the first time you use it, so the reader never has to leave the sentence.
- Or link the first mention to a definition, which is the other documented route.
- Build a glossary and make it reachable from the site's ordinary navigation, which satisfies the rule without a link on every occurrence.
- Prefer the plain word wherever one exists and does the same job.
Step-by-step fix guides (7)
- H40: Mark up term-and-definition pairs as description lists
- H54: Mark the defining instance of a term with dfn
- G55: Link unusual words to their definitions
- G62: Provide a glossary for specialized terms
- G70: Offer a dictionary search for specialized content
- G101: Define words used in an unusual or restricted way
- G112: Define specialized terms inline where they appear
Passes vs. fails
Passes
The same sentence links ACR and VPAT to their definitions, so a reader who has met neither can look them up without leaving the page.
Fails
A page tells the reader to make sure their ACR reflects their VPAT edition, and defines neither term anywhere.
In audits and lawsuits
This is Level AAA, so it falls outside our audit scope and outside every legal obligation we track. W3C still encourages it below AAA, in as many words, for specialized information written for non-specialist readers, even where you are claiming only A or AA. It is also the criterion that makes the case for a glossary. One detail is worth having before you build one. A glossary satisfies this on its own when a reader can find it through the site's ordinary navigation, so linking every occurrence in the prose is good practice rather than the requirement. It stops working the moment one word carries two definitions on the same page, and then only a per-occurrence definition will do. Keep this separate from Reading Level below. This one is about particular words. That one is about the difficulty of the sentences carrying them.