If you've seen "a11y" floating around the web development space and you're not sure what it means or how to say it, you're absolutely not alone. Don't feel bad! Almost no one knows what it is until someone else tells them. I didn't know for a long time. I even created a tool that relies on the mispronunciation of it!
"A11y" is a numeronym or number-based word. It is composed of three parts:
"a"- the first letter of the word "accessibility"
"11"- the number of letters between the first and last letters of the word "accessibility"
"y"- the last letter of the word "accessibility"
Numeronyms are very common in web development! Think of "K8s" (Kubernetes), "i18n" (internationalization), and "o11y" (observability) as a few of examples. Some of them have different pronunciations depending on how the number in the middle is pronounced in combination with the letters before and after it.
The way we pronounce "K8s" is different than the way we pronounce "a11y" because of how the numbers flow with the other letters. We could pronounce "K8s" as "kay-eight-ess", but "keights" (see the word eight in the middle?) is a single syllable and a little easier to say.
So how to do we pronounce "a11y"? We say "ay-eleven-why". Pronunciations like "al-ee" or "al-eye" don't quite fit like most other pronunciations of numeronyms because they're not saying the number in the middle at all. This isn't to say that all numeronyms are said the same way, but most that use this format follow this idea.
Numeronyms are often used when their original word is a lot of characters or difficult to pronounce. According to Wikipedia, the first numeronym was created in the 1980s for a software account owner's surname because it was too long for the system to handle. "Accessibility" is 6 syllables whereas its numeronym is 1 less. That's not a huge amount of savings, but the phonetics of "a11y" are easier for many people to verbalize than "accessibility" because the there are less "harsh" syllables in comparison.
Numeronyms are also helpful where brevity is important, such as in tweets because Twitter enforces a character maximum. Since there are less characters to type, it can also be more efficient once you get used to using it. For me personally, it's also easier to remember how to spell!
Do I have to use it?
Nope! If you like using the word "accessibility" more than you like using the "a11y" numeronym, please continue to do so. It's definitely a matter of preference and using one or the other does not make you more or less knowledgeable. If someone tells you otherwise, they are unfairly gatekeeping the topic of web accessibility. What truly matters is that you know what "a11y" means so you're not thrown off when you read it in other people's content.
Remember: everyone has different accessibility needs. Some people use "a11y" because it's more accessible to them. If "accessibility" is more accessible to you, that's totally acceptable!