token
A small piece of text, often part of a word, that language models read and write.
Language models do not read letters or whole words. They split text into tokens, which are common chunks such as "play", "ing" or "the". A short English word is usually one token, and a long word may be two or three. Models are priced, limited and timed in tokens, so the idea matters when comparing tools.
Think of it as
Like Lego bricks for text. A sentence is built from standard pieces, and the model reads and writes brick by brick rather than letter by letter.
Example
The sentence "Your order has shipped" is about five tokens. A service that charges per million tokens is really charging for how much text goes in and out, which is why long documents cost more to process.