Armageddon: the symbolic place where the kings of the world are gathered for the final battle against God
This is a place name that the book of Revelation invents and uses exactly once. Revelation marks it as a Hebrew word, then describes the unclean spirits gathering all the world's kings to it for the great day of God Almighty. So the word names a location, but the location is a picture, not a dot on a map.
The name almost certainly echoes Megiddo (מְגִדּוֹ), an ancient city on the plain of Jezreel where some of Israel's most famous and most bitter battles were fought, including the defeat that killed good King Josiah. Revelation calls it a mount, yet there is no Mount Megiddo (מְגִדּוֹ), which is the first clue that the writer is reaching for memory and resonance rather than coordinates. Other Hebrew phrases seem to ring inside the word as well: the cosmic mountain where God's enemies gather to be judged (מועד), and the destroying mountain that Babylon is called when she herself is about to be cut down.
Most scholars read it the way they read Revelation's other loaded names, like Babylon, Sodom, and the Euphrates. Each one is a theological cipher built out of Old Testament memory rather than a literal address. Armageddon condenses every Hebrew tradition of an end-time mustering of the nations for judgment into one ominous word, and the writer never resolves it to a single place precisely so it can sound on several frequencies at once.
In Revelation's own structure the verse does not describe a battle at all. It describes a gathering. The actual confrontation comes later, and the same gathering, the same kings, and the same Old Testament backdrop return there, so Armageddon names the staging point of the last conflict between evil and God, wherever and however that conflict is finally pictured.