What does “a11y” mean?

When researching web accessibility online it is common to see a strange combination of letters and numbers, “a11y.” This is the accepted short version of the word “accessibility.” It is sometimes used in social media to tag posts as accessibility content where space is a premium, such as Twitter.

The abbreviation is derived by taking the 13 letters in “accessibility” and replacing the middle 11 letters with “11.” By keeping the first and last letters “a” and “y” the end result is a reduction of nine letters. a + 11 + y  = a11y.