A book (also sometimes called a monograph) is a set of pages fastened along one side and encased between protective covers; a collection of leaves of paper, parchment, vellum, or other material (whether written, printed, or blank), affixed in some manner to one another, with or without a case or cover. It can also refer to a literary work or one of its volumes.
The U.S. Postal Service defines a book as a publication qualifying for the fourth-class postal rate consisting of 24 or more pages, at least 22 of which bear printing, which contains primary reading material, with advertising limited to book announcements. According to UNESCO, it is a non periodical literary publication consisting of 49 or more pages.