a book can be a text that is a part of a larger collection of texts. a section of a text may be published as a book so that it only has one author or only focus on one subject area. books written in this way can be understood without reading whole collection of writings. examples are the iliad, odyssey, bible, quran and torah. 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 are published as separate volumes. each volume is a book.