"Mulder and Scully were outsider heroes working within a corrupt government, and their questing to expose truth and squelch the apocalypse resonated with the alt-culture vibe and premillennial angst of the 1990s." —Jeff Jensen, Entertainment Weekly, 3 July 2015
When we hear the word apocalypse, a number of images run through our minds: fire and flood, earthquakes and tidal waves, crumbling societies, zombies. But when apocalypse came into English in the 1200s, it referred to none of these things.
Apocalypse was initially used to refer to a particular type of Jewish and Christian writing that was common between 200 BC and 150 AD and which used symbolic imagery usually to foretell the end of this world and the future to come. The best-known apocalyptic work is the Apocalypse of St. John of Patmos, more commonly called the book of Revelation.
The Greek word that gave us apocalypse means "to uncover" or "to reveal." You can see how the Apocalypse of St. John came to be called Revelation, then: the apocalyptic writings were so called because they revealed or uncovered future events.
Apocalyptic writings, and especially the Apocalypse of St. John, were often filled with cataclysmic events that heralded the end of this present age and the dawning of the age to come: fires, earthquakes, heavenly armies fighting. A few centuries after the word apocalypse entered English to name this style of literature, the word gained two additional senses: one that referred to the final battle between good and evil that's spoken about in the Apocalypse of St. John, and another to refer to any great disaster with far-reaching effects.
This last meaning, so far removed from the original use that referred to a type of literature, is now the most common use of apocalypse, and has even shown up in humorous portmanteaus—most notably in snowpocalypse to refer to a sizeable snowstorm.