Armageddon was, according to various races and groups, the end of existence. The word was derived from a Bible passage.
In 2268, James Kirk gave the stardate as "Armageddon" in his captain's log after the Beta XII-A entity had taken over the crew of USS Enterprise, causing hate to manifest in everyone. (TOS: "Day of the Dove")
In 2285, Doctor Leonard McCoy considered the Genesis Device to be a potential creator of "universal Armageddon". (Star Trek II: The Wrath of Khan)
In 2373, the Dominion attempted to destroy the Bajor sector, Deep Space 9 and several Federation, Romulan, and Klingon starships by igniting a trilithium, tekasite, and protomatter bomb in the Bajoran sun. After this attempt was thwarted, Benjamin Sisko said that "Armageddon will have to wait for another day". (DS9: "By Inferno's Light")