A '''book''' ([[Spanish language|Spanish]]: ''libro'', [[French language|French]]: ''livre'', [[German language|German]]: ''Buch'', [[Dutch language|Dutch]]: ''boek'', [[Greek language|Greek]]: βιβλίο, [[Russian language|Russian]]: книга) is a collection of written words, usually on paper but increasingly being found in electronic formats such as Kindles and iPads. The [[Bible]] is an example of a book (in fact, the word "Bible" is derived from the Greek word for "book."), as well as a collection of books. Books are often used for educational purposes in the form of text books, although there is concern about the accuracy of the information contain in some of them. Any finite collection of books can be bound together to form a new book.
The average length of a best-selling book has been sharply decreasing, falling by nearly 50% in merely seven years: in 2011, average length of a bestseller was 467 pages, but by 2017 that length had declined to 273 pages.<ref>https://scribemedia.com/how-long-should-book-be/</ref> But some observe that book length has at times increased in the last quarter-century.<ref>https://www.theguardian.com/books/2015/dec/10/are-books-getting-longer-survey-marlon-james-hanya-yanagihara</ref>
The book was called a [[codex]] in Latin, and it was a [[Roman]] improvement over the scroll. By the fourth century the codex had gained wide acceptance, and many scrolls that were not converted to codex form were lost to posterity.