What is a token in the context of a large language model $($LLM$)?$

A$.$ The part of the LLM output that has primarily symbolic rather than substantive value $($as in$,$the court issued a token fine$,$ or $$the LLM generated a token output$).$

B$.$ A word or part of a word in either the input prompt or LLM output.

C$.$ A physical device or digital code to authenticate a user$$s identity.

D$.$ A unit of cryptocurrency $($like bitcoin or other $$crypto tokens$)$ that you can use to pay for LLM services.