DM

DM could be an acronym for one of the following:
 * Instances
 * Deadmines
 * Dire Maul
 * Armor sets
 * Dreadmist Raiment, warlock's Dungeon Set 1.
 * Deathmist Raiment, warlock's Dungeon Set 2.
 * Other
 * DamageMeters, an AddOn that measures player and teammates' damage, healing, and tanking statistics.
 * Dungeon Master, a misnomer for Game Master.

Dire Maul vs The Deadmines
Post-Cataclysm, the loss of Shen'dralar faction reputation has all but eliminated any reason to run Dire Maul for characters at the level cap, while level 85 characters have the option to run Deadmines at heroic level.

Therefore, DM now almost exclusively refers to Deadmines now, although some players will still refer to it as VC.