Apocalyptic fiction is a subgenre of science fiction that is concerned with the end of civilization due to a potentially existential catastrophe such as nuclear warfare, pandemic, extraterrestrial attack, impact event, cybernetic revolt, technological singularity, dysgenics, supernatural phenomena, divine judgment, climate change, resource depletion or some other general disaster. Post-apocalyptic fiction is set in a world or civilization after such a disaster. The time frame may be immediately after the catastrophe, focusing on the travails or psychology of survivors, or considerably later, often including the theme that the existence of pre-catastrophe civilization has been forgotten (or mythologized).
Apocalypse is a Greek word referring to the end of the world. Apocalypticism is the religious belief that there will be an apocalypse, a term which originally referred to a revelation of God's will, but now usually refers to belief that the world will come to an end very soon, even within one's own lifetime.
Apocalyptic fiction does not portray catastrophes, or disasters, or near-disasters that do not result in apocalypse. A threat of an apocalypse does not make a piece of fiction apocalyptic. For example, Armageddon and Deep Impact are considered disaster films and not apocalyptic fiction because, although Earth or humankind are terribly threatened, in the end they manage to avoid destruction. Apocalyptic fiction is not the same as fiction that provides visions of a dystopian future. George Orwell's Nineteen Eighty-Four, for example, is dystopian fiction, not apocalyptic fiction.