From DMJ Productions

A book is a medium for recording information in the form of writing or images. Books are typically composed of many pages, bound together and protected by a cover. Modern bound books were preceded by many other written mediums, such as the codex and the scroll. The book publishing process is the series of steps involved in their creation and dissemination.

As a conceptual object, a book typically refers to a written work of substantial length, which may be distributed either physically or in digital forms like ebooks.

From Wikipedia