A book is ‘a written or printed work consisting of pages glued or sewn together along one side and bound in covers’ (Oxford Dictionary). This is a definition too broad and too narrow.
It is too broad because history shows that books can exist in many forms. The definition is referring to a book – form called codex. Books in the ancient time were in scrolls made of papyrus. Imagine the grand opening of the first public library in the Roman Empire, the shelves were packed not with bound books but rolls and rolls of scrolls to be kept under a dry condition.