@IamAcand @feditips
If you follow the tag you'll find posts about digital accessibility. 'a11y' is a #numeronym for 'accessibility'. It dates back to 140 character Twitter & it's how most folks posting about accessibility tag their posts.

Numeronyms use the first & last characters of a term to bookend a numeral representing the number of characters in between. E.g. 'accessibility' reduced to 'a11y', which is a big deal if your trying to communicate in coherent 140 or 280 char chunks.