A basic definition of apocalyptic cinema is a motion picture that depicts a credible threat to the continuing existence of humankind as a species or the existence of Earth as a planet capable of supporting human life. The genre of apocalyptic cinema is closely related to, yet distinct from, a similar genre primarily known as post-apocalyptic cinema, which concentrates on survivors of a catastrophic event struggling to reestablish a livable society. In order to be classified as an apocalyptic film, the event threatening the extinction of humanity has to be presented within the story. If this catastrophe occurs prior to the events depicted on the screen, the film is post-apocalyptic. Naturally there can be a blurring of the lines of these two genres, and a number of pictures can legitimately be labeled as both. In Deluge (1933), for example, the first half of the story is clearly apocalyptic and the second half is post-apocalyptic. The same is true of the television mini-series based on the novel The Stand by Stephen King. The first episode is apocalyptic while the remaining three episodes are post-apocalyptic. Two novels by Philip Wylie and Edwin Balmer also serve to illustrate the difference. When Worlds Collide is apocalyptic, and After Worlds Collide is post-apocalyptic. Unfortunately in general criticism, the distinctions between apocalyptic and post-apocalyptic categories are often been overlooked.
Apocalyptic films can be classified into seven specific categories: Religious or Supernatural; Celestial Collision; Solar or Orbital Disruption; Nuclear War and Radioactive Fallout; Germ Warfare or Pestilence; Alien Device or Invasion; and Scientific Miscalculation. An eighth category, Miscellaneous, is somewhat of a grab bag that required to account for a few oddball titles outside these regular categories. A few films, such as Virus (1980), combine elements from several categories. A close examination of each grouping defines the unusual scope and breadth of the apocalyptic genre.