refers to the smallest, standard physical unit of paper in a printed piece; in the case of books and pamphlets, usually with a printed page on each side of a leaf; a broadside is printed on a single side of a single leaf.

What is to take a leaf out of?

to copy something that someone else does because it will bring you advantages: Maybe I should take a leaf out of Rick’s book and start coming in early every morning.

What does it mean to take a page out of someone's book?

take a page out of (someone’s) book To do something in the way someone else would do it; to behave or act like someone else. I think I’m going to take a page out of your book and start going for a run first thing in the morning.