A book is a written work of substantial length by one or more authors. They can be distributed in various forms including as printed books, audiobooks, and electronic books (ebooks). Books are broadly classified into fiction (containing invented content, often narratives) and non-fiction (containing content intended as factual truth).
The term can also refer to the physical or electronic object that contains such a work. Modern printed books are typically composed of many pages bound together and protected by a cover. This is known as the codex format. Codices have been created for centuries and were used even before printed books were available to create manuscript books by hand. Older formats include scrolls and clay tablets.