It's a common term that most people use to mean "the end of the world," but it's true meaning is a little bit different.
The Bible mentions Armageddon only once, in Revelation 16:16: "And they gathered them together to the place called in Hebrew, Armageddon." The Greek word Armageddon comes from two Hebrew words: Har Megiddo, meaning "the hill of Megiddo."
The common (but misleading) notion is that Armageddon will be the last, climactic battle to be fought on earth between the powers of good and evil. However, this is not quite right in several crucial respects.
Armageddon—or more likely the large broad Valley of Jezreel, or Esdraelon, which Megiddo overlooks—will in fact be the staging area for the final great battle of this age, but not the site of the battle itself. That is set not at Meggido but in the Valley of Jehoshaphat—commonly reckoned to be the Kidron Valley, immediately adjacent to Jerusalem (see Joel 3:2, 9-16).
Notwithstanding the popular concept of the Battle of Armageddon, the Bible makes no specific prediction for a war fought at Armageddon between two human armies precisely at Christ’s return. However, the Bible does say that the armies of the East and West will be drawn to the infamous valley by lying demons (Revelation 16:14). From there they will march to Jerusalem. There they will fight the returning Jesus Christ (Revelation 14:14-20; 16:14; 19:11-21; Joel 3:12-14). GN
