Folios are a type of bookbinding that is used to bind large documents such as manuscripts, maps, and other documents. The term 'folios' comes from the Latin word for 'LEAF, ' and it refers to the leaves of paper that are bound together in a book. In the library, folios are often used to store and protect valuable documents. Leaves in the library, then, refer to the folios that are used to store and protect documents in the library.