From the game of Diplomacy, a DMZ (De-Militarized Zone) is a territory where two or more players agree not to enter without previous consent of the others.

This agreement is usually made to avoid conflict in critical spots of the game board, specially in the early game where alliances are not yet defined, but also on the late game where keeping a strong long-lasting alliance is critical.

The player who invades a DMZ is said to have 'broken' it and is usually seen as an agressor.