From Wikipedia

Countdown to Armageddon

Armageddon (Late Latin: Armagedōn, Ancient Greek: Ἁρμαγεδών Harmagedōn, Hebrew: הר מגידו‎ har məgiddô) is the site of an epic battle associated with the end time prophecies of the Abrahamic religions.

According to traditional Christian interpretations, the Messiah, the "Lamb", will return to earth and defeat the Antichrist, the "Beast", in the battle of Armageddon. Then Satan will be put into the bottomless pit or abyss for 1,000 years, known as the Millennial age. After being released from the abyss, the Satan will gather Gog and Magog from the four corners of the earth. They will encamp surrounding the holy ones and the "beloved city". Fire will come down from God, out of heaven and devour Gog and Magog at the Armageddon, and the Devil who deceived them is thrown into Gehenna (the lake of fire and brimstone) where the Beast and the false prophet have been since just before the 1,000 years.

The word Armageddon appears only once in the Greek New Testament. The word comes from Hebrew har məgiddô (הר מגידו), meaning "Mountain of Megiddo". Megiddo was the location of many decisive battles in ancient times (see Battle of Megiddo). The town Megiddo is approximately 25 miles (40 km) west of the southern tip of the Sea of Galilee (or Lake Tiberias to the Romans) in the Kishon River area.