The way we define those items that are commonly known of as "books" is rapidly changing. Traditionally, a book was a collection of printed (or written) paper sheets fastened together as a specific, and often expensive, artifact. Most people would refer to a book as something printed and bound, with a collective purpose or overall meaning. A book could be in one of a number of genres. Nonfiction books generally present factual information, while fiction tends to present a story with its own integral progression and meaning.
However, nowadays what we refer to as a book or books doesn't have to be printed, or written, and paper need not be involved at all. There are ebooks, which are electronic texts available to be read on an electronic device such as a computer, ebook reader, or some kind of handheld device like a PDA. There are hypertext "books" which follow varying paths and may have different plots, varied objectives, and even stories that blur the lines between author and reader. There are audio Books which consist solely of spoken word, and books that combine a range of audio visual elements and text. Books can be borrowed from the library, read online, purchased and kept, or shared, played with, read, and deleted.