Armageddon

occurs only in [(Rev 16:16) (R.V., "Har-Magedon")], as symbolically designating the place where the "battle of that great day of God Almighty" (Rev 16:14) shall be fought. The word properly means the "mount of Megiddo." It is the scene of the final conflict between Christ and Antichrist. The idea of such a scene was suggested by the Old Testament great battle-field, the plain of Esdraelon (q.v.).

EBD - Easton's Bible Dictionary