Aggro

aggro, v., adv., MMORPG-ism: On Everquest and other MMORPGs, a mob becoming aggressive and attacking a PC or (less often) another mob.
Ex: I was kiting two bandits and ran too close to three others. They aggroed on me and I got kacked. [GJ1]
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Addendum: This term reaches back into MUDs, and predates EQ by quite a bit. [DV]
Addendum #2: The term is from the word "aggressive", originating on MUDs. A mob that had been attacked would turn aggressive-mode on the attacker, and remain thus even if the character died; if someone bit off more than he could chew and was killed or chased away, he would usually ask for help in dealing with the now-aggro mob. [K]