Aggro is the level of aggressive attention a given player has gained from enemy AI, or in some cases the act of getting that aggressive attention. When a player character has aggro from an enemy, that enemy will focus its attention and attacks on the player character. The term is commonly used in MMOs, where aggro plays a pivotal role in party-based combat, and is almost always used in PvE context, an almost never used in PvP context. This is because aggro is specifically a term used to describe (and thereby exploit) an AI behavior.