What is a Book?

I have already done some previous posts on this question.
But thought i would write what my first impressions of the work Book are.

A book is a group of pages bound together.
It could be Hardback or paper.
The content could be : Fictional, Stories, Personal - Dairies/Journals/Sketchbooks. Informative, Photos (Albums) , Records - e.g Doctor keeps a record of your medical History in a file.
Is a book always paper based? You could have a book on the computer, a folder of files? A database? Is there such thing as a virtual Book, does it need to have a physical feel to it?
The most well known book? I would say The Bible is possibly the only book that everyone worldwide knows, or who has at least heard of.