What does it mean to book someone?

To "book" someone is a police slang term for recording their arrest on the agencies Arrest Log. "Booking" is the process by which a person is logged into the jail after arrest. Typically, this process involves a search, trading your clothes for a jail uniform, and having your photos (mug shots) and finger prints taken.

You would then be housed until you are bonded (or 'ROR'd) out or until trial.