Armageddon

Armageddon (pronounced ahr-muh-ged-n)

(1) The place where the final battle will be fought between the forces of good and evil.

(2) The last and completely destructive battle; the scene of a decisive conflict on a great scale; any great and crucial conflict. 

(3) A catastrophic and extremely destructive conflict.

(4) In chess, as "armageddon round", an arrangement in some competitions used when a match would otherwise end in a draw, the rules being (1) black wins drawn games and (2) white is granted more time in compensation.

From the biblical Book of Revelation (New Testament 16:16) and the familiar modern use in the figurative sense of a final conflict apparently dates only from 1811.  The actual word was from the Late Latin Armagedōn, from the Ancient Greek Ἁρμαγεδών (Harmagedōn)), from the Hebrew הר מגידו or ‎הַר‎ מְגִדּוֹ‎ (har megiddo) (Mount of Megiddo), the mountain district of Megiddo, in northern Palestine, site of a number of battles mentioned in the Old Testament, most notably that associated with the Last Judgment.

The Last Judgment (circa 1488), triptych by Hieronymus Bosch (circa 1450–1516).

In the Book of Revelation, Armageddon is the prophesied location of a gathering of armies for a battle at the end of times.  Theologically, the western consensus is to interpret this as the battle between good and evil, often expressed as between God and the Kings on earth (Revelation, 16:14).  However, most biblical scholars regard the text as highly symbolic (even cryptic), regarding Mount Armageddon as an idealized location, concluding the final battle between good and evil, while inevitable, may well take place in some other location.  Others are more specific, a sect called the Dispensationalists suggests Armageddon will be a campaign (sometimes dramatically styled as the war of a thousand years) and not a specific battle.  All however agree it will be fought in and for the lands we call the Middle East.

Also disclosed in Revelation is the number of the Beast (Revelation 13:15–18).  In most English translations the number of the beast is 666 (although some early Greek translations prefer 616).

Then I saw another beast coming up out of the earth, and he had two horns like a lamb and spoke like a dragon. And he exercises all the authority of the first beast in his presence, and causes the earth and those who dwell in it to worship the first beast, whose deadly wound was healed.  He performs great signs, so that he even makes fire come down from heaven on the earth in the sight of men.

And he deceives those who dwell on the earth by those signs which he was granted to do in the sight of the beast, telling those who dwell on the earth to make an image to the beast who was wounded by the sword and lived.  He was granted power to give breath to the image of the beast, that the image of the beast should both speak and cause as many as would not worship the image of the beast to be killed.

He causes all, both small and great, rich and poor, free and slave, to receive a mark on their right hand or on their foreheads and that no one may buy or sell except one who has the mark or the name of the beast, or the number of his name.

Here is wisdom. Let him who has understanding calculate the number of the beast, for it is the number of a man: His number is 666.

The unfortunate condition Hexakosioihexekontahexaphobia is the fear of the number 666.  It's said to be rare.