There are also many definitions on what a "book" is. Is a business book a book? Is a self-improvement book a book? Or are there only fiction books? How about e-

There are also many definitions on what a "book" is. Is a business book a book? Is a self-improvement book a book? Or are there only fiction books? How about e-books? Is there a size limit under which a text is not a "book" anymore? Depending on such points everybody might be already reading 60 books a year without even realizing it.