A book is a collection of written, printed, illustrated, or blank sheets, made of paper, parchment, or additional material, generally fastened together to center at one side. A single sheet inside a book is called a leaf, and each side of a leaf is called a page. A book produced in electronic format is called an e-book.

Books may as well refer to a literature work, otherwise a main division of such a work. In library and information science, a book is known as a monograph, to differentiate it from serial periodicals like magazines, journals or newspapers. The body of all written works with books is literature.