A book can also be a text in a larger collection of texts. That way a "book" is perhaps written by one author, or it only treats one subject area. Books in this sense can often be understood without knowing the whole collection. Examples are the Bible, the Quran all of them consist of a number of “religious books” in this sense of the word. Encyclopedias often have separate articles written by different people, and published as separate volumes. Each volume is a book.