Bible Meaning: Hill (city) of Megiddo, the mount of Megiddo
Strong's Concordance #G717
The Megiddo part of Armageddon means "cut off" or slaughter. The city, located in the valley of Jezreel, was given to the tribe of Manasseh (Joshua 17:11) as an inheritance in the Promised Land. Previous to it being conquered it was a Canaanite royal city (Joshua 12:21).
Scripture states that it is in Armageddon (the valley of Jezreel where Megiddo is located) where man's last war will occur. The world's armies, gathered by the Antichrist (a human possessed by Satan the devil), will fight the return of Jesus Christ as he is coming back to the earth.
Important Armageddon verses
Revelation 16:12 - 14, 16
And the sixth angel poured out his vial upon the great river Euphrates; and the water thereof was dried up, that the way of the kings of the east might be prepared.
And I saw three unclean spirits like frogs come out of the mouth of the dragon, and out of the mouth of the beast, and out of the mouth of the false prophet.
For they are the spirits of devils, working miracles, which go forth unto the kings of the earth and of the whole world, to gather them to the battle of that great day of God Almighty.
And he gathered them together into a place called in the Hebrew tongue Armageddon.