What is a book?

The term "book" may indicate,

• A collection of paper leaves bound together.
  
• A number of written or printed sheets fastened together at the back by means of some kind of cover known as binding.
  
• A literary treatise, usually written or printed in one volume, but sometimes in several volumes if forming a single work.
  
• A literary work
  
• Main parts of a literary production (e.g the Iliad consists of 24 "books")
  

The actual origin of the word "book" was from an Old English work for "beech tree", boc. The connection between "book" and "beech tree" was probably that the English monks wrote their books on white beech tablets. More probable is the following theory: Old English boc means "charter", and its plural means "tablets, writing tablets, written sheets"; hence, supposedly "book".

On the other hand, the term "book" derives from the German word Buch, meaning "beech", and is connected with the fact that, in early days, beech wood was largely used for binding books. The beechen covers "were light decorative and very carefully dried and seasoned..." (C. Davenport).

Extracted from: Diringer, David. The Book Before Printing Ancient, Medieval and Oriental. NY:Dover Publications, 1982. P.24-25.