Audiobooks or "talking books" are books that have been read aloud by someone and recorded. Nowadays, they are usually recorded onto compact discs (CDs), although some older editions remain on cassette tapes. (This is why many texts in this format were first called books-on-tape.) More recently, audiobooks have been available to download from the internet (free or paid-for) and pre-recorded on special MP3 players.
Many popular books are often chosen to be turned into audiobooks. The original author may or may not be involved in choosing the narrator for the reading. Some authors often use the same reader for many books, so that their audiobooks have a similar sound or style.