crib notes; cheat sheet; study guide
Slang term for a condensed reference or answer key, often used by students. Can refer to a physical booklet or digital notes. The 'key' gloss applies to explanatory diagrams or maps.
I got a cheat sheet from a friend before the exam.
If you look at this key, you can quickly understand the symbols on the circuit diagram.
A shortened form of 虎の巻, originally referring to the 虎韜 section of the ancient Chinese military work 六韜 and later to a secret manual, study guide, or set of crib notes.