Token
The small chunk of text an AI reads and writes in — about a word or part of one — and the unit AI usage is measured in.
A token is a piece of text — often a whole word, sometimes just part of one — that an AI breaks language into so it can process it. A short sentence might be a dozen or so tokens. It's the AI equivalent of counting words or characters, just in the units the model actually uses.
Tokens matter for two practical reasons: cost and length. AI usage is usually priced and limited by the number of tokens read and written, and each model can only handle so many at once. You rarely need to think about tokens directly, but it's why very long documents sometimes get summarized or split into parts.
Why it matters
Tokens are the meter AI runs on, so they quietly drive what AI tools cost and how much text they can handle in one pass.