A version of the word Armageddon is only found in one place in the Bible,

Rev 16:16
"And they gathered them together to the place which in Hebrew is called Har-Magadon (Armageddon)".

Armageddon is the final event of the Tribulation.  It is when all the armies of the earth gather to come against Israel and to eradicate the Jewish people.

Mark Hitchcock gives a proposed chronology of the events leading up to Armageddon as presented by Scripture:

• Phase 1:The Euphrates River dries up to prepare the way for the kings of the east (Rev 16:12).
• Phase 2: The allies of the Antichrist assemble in preparation to go against Israel (Rev 16:12-16).
• Phase 3: The armies of the Antichrist attack Jerusalem and conquer the city (Zech. 14:1-3).
• Phase 4: Jesus Christ returns to the Mount of Olives (Zech. 14:4).
• Phase 5: Christ and His armies destroy the armies gathered against Jerusalem in the valley of Jehoshaphat (Joel 3:9-17, Zech. 12:1-9, 14:3).
• Phase 6: Christ destroys Edom and delivers the Jewish people around the city of Petra (Isaiah 34:1-7; 63:1-5;, Joel 3:19).
• Phase 7: At Armageddon, the Antichrist rallies his armies to fight against the Lord Jesus and His armies (Rev 16:16; 19:19-21).

Christ and his armies win the war and the Antichrist and false prophet are cast into the lake of fire (Rev 19:20).