Is a physical piece of paper often filled with equation or facts in compressed writting,Most of students use it during their examinations to improve their marks especially history students because they learn many histries,same as programming because users use it to cheat if they are dealing with something challenging.
Cheat-sheet contains information like let say your creating a webpage to other company and you forgot how to use cascading style ,jquery and you go back to html turtorial to look for a solution and continue with your webpage.
Many computer applications have cheat-sheets iincluded their documentation which liist keystrokes or menu commands needed to achieve specific task.
Cheat sheet allows you achieve specific task if you are dealing with complex things because you can not remember everything somethimes you find that you are dealing with difficult thing you can go back and find the solution.