The term a11y is a numeronym for the word accessibility. A numeronym is a shorthand where numbers replace some letters in a word while keeping the first and last letters intact. In this case, the 11 in a11y represents the eleven letters between an and y in accessibility.
This abbreviation became popular within the tech and digital accessibility communities as a way to quickly refer to accessibility in discussions, documentation, and online conversations. It follows a pattern seen in other well-known numeronyms, such as i18n for internationalisation (18 letters between i and n) and l10n for localisation (10 letters between an and y.
Beyond just being a shorthand, a11y has grown into a widely recognized symbol of digital inclusivity, representing the efforts to make websites, applications, and digital content accessible to all users, including those with disabilities. The term is now commonly used in hashtags, conferences, and initiatives that promote best practices in accessibility.