The Book of Revelation, also called Revelation to John or Apocalypse of John, (literally, apocalypse of John; Greek, Αποκαλυψις Ιωαννου, Apokalupsis Iōannou) (IPA: [əˈpɑkəlɪps]) is the last canonical book of the New Testament in the Bible. It is the only biblical book that is wholly composed of apocalyptic literature. The visions given in this book were future events for the understanding of the early church, primarily.
(Summary from Wikipedia and Sam Stinson)