From the Greek apokalupsis, 'a revelation'. The term Apocalypse refers to the last book of the Bible, the Book of Revelation. This sets out a vision of the upheavals attending the end of the world and the Last Judgement as revealed to Saint John on the island of Patmos.
Apocalyptic images are usually related to this vision, although the word has now acquired a wider meaning and can be used in reference to any prediction of upheavals with dire consequences.
