background information on something or someone; basic facts in order to get a take (probably from “glossary”, the part of a book which lists sources of information)

Byden might be making an announcement and he'll take off his jacket, and the green jacket will be on underneath, or someone will jump out from under the prefects' desk wearing it. Something like that.

It requires a fertile and high-functioning brain to take something as simple as the truth and twist it, palming off the deception on someone else with the earnestness of a choirboy.