Digital accessibility is the practice of making digital things usable by people with disabilities: sites, apps, documents, email, kiosks. The word covers a wider scope than web accessibility, which is why it turns up in job titles and procurement documents. This page is the vocabulary a business meets in its first fortnight on this subject, including the numeronym everybody uses and the conformance level almost nobody should aim at.
The word, and the numeronym
a11y is accessibility with the eleven letters between the a and the y replaced by their count, the same joke as i18n for internationalisation. It is used everywhere in the field's tooling and job titles. Digital accessibility is the umbrella; web accessibility is the part about sites; document accessibility is the part about files. All three are measured against the same guidelines.
Cognitive accessibility, which the criteria under-serve
Much of WCAG addresses vision, hearing and motor disability well and cognitive and learning disability less directly. The practices that help are plain language, consistent navigation, forms that forgive errors, and not relying on memory or time limits. The W3C's own guidance on making content usable for cognitive and learning disabilities is the reference here, and most of it improves the site for everybody.
Level AAA, and why AA is the target
WCAG defines three conformance levels. AA is what regulators, procurement and courts point at, and it is what the 50 A and AA criteria in WCAG 2.2 cover. AAA includes criteria that cannot be met by all content, which is why the guidelines themselves say a whole site should not aim at it. Meet AA, then adopt individual AAA criteria where they help.
Questions people ask about what is digital accessibility
Is a11y the same as accessibility?
Yes, it is the field's shorthand for the same word.
Should we aim at AAA?
No, for most sites. Meet AA and adopt individual AAA criteria such as higher contrast where they are easy.
Does accessibility help SEO?
Some of it overlaps, chiefly structure and alt text. That is a side effect and not the reason to do it.