Apocalyptic literature is a genre of prophetical writing that developed in post-Exilic Jewish culture and was popular among millennialist early Christians. "Apocalypse" (Ἀποκάλυψις) is a Greek word meaning "revelation", "an unveiling or unfolding of things not previously known and which could not be known apart from the unveiling." The apocalyptic literature of Judaism and Christianity embraces a considerable period, from the centuries following the exile down to the close of the middle ages.