cheat sheet

Short definition from Wiktionary

Noun

1. 1
   A sheet of paper (or a digital analogue thereof) containing notes used to assist (with or without permission) on a test; especially, such a sheet used secretly and improperly.
2. 2
   Any summary or quick reference used as a shortcut or reminder, such as an aid for public speaking.
3. 3
   Alternative spelling of cheat sheet.