Tokenziation

Tokenization is a way to break down a string of continuous text into small individual chunks called tokens, each token can be a word/character/sub-word.

Different tokenization schemes can be used based on different aspects.

So let's say your tokenizer divided the whole text corpus into $T$ tokens i.e. there are your text is divided into total $T$chunks of smaller words, characters, sub-words, etc. Now this $T$ becomes the Vocabulary size of your model.

Each token has an token_id $\in [1, T]$.

Tokenizers - Hugging Face NLP Coursehuggingface