The word Armageddon is found only once in the King James Bible (Revelation 16:16). It is derived from a Greek term spelled the same as its English counterpart (Strong's Concordance #G717). The Greek itself, however, is a compound term taken from two Hebrews words. The first part is derived is har (#H2022), which means a mountain or a range of hills, followed by Megiddo (or megiddon), the name of a location in ancient Israel. Together, Har-Megiddo (Armageddon) means the mount of Megiddo.
For they (three unclean spirits) 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 (Revelation 16:14, 16).
Armageddon, or har-megiddo, is a small hill (mount) located near Megiddo in the northern part of modern-day Israel. It and the area that surrounds it was initially given to Israel's tribe of Manasseh as an inheritance in the Promised Land (Joshua 17:11). The mount, located within the valley of Jezreel, is where ancient forts were built that guarded the main highway that connected Ancient Egypt with Mesopotamia.
It is in the broad valley of Jezreel that the world's last global conflict will take place. Revelation 16:16 references the climactic battle between good (Jesus and his resurrected saints) and evil (the Antichrist along with his deceived army of humans). This unique event will occur during the Lord's Second Coming.
The word Armageddon, however, has come to mean more than the location of mankind's last stand. It is frequently used to label the entire period starting from when the armies of the world begin to gather together (along with the beast and false prophet) to fight Jesus to his actual return and victorious war over the forces of evil. It is after this victory that Christ sets up His Millennial Kingdom on the earth.
The overall purpose of the book of Revelation is, "to shew unto his servants things which must shortly come to pass" (Revelation 1:1). The word armageddon, given the book's focus on the cataclysmic events soon to take place around the entire world, has also been used in reference to this entire prophetic section of Scripture.