is derived from the words "ANGRY". It shows the radius in which monsters who you are getting close to will attack you. If your aggro is big, you will attract monsters from a higher distance. Read more in the other topics.


While this is the minor definition, we have the following from wowwiki:

"
Aggro is a jargon word in WoW, probably originally derived from the English word "aggression" and used since at least the 1960's in British slang. In MMORPGs such as WoW, "aggro" can be either a noun or a verb referring to the possibility of a computer-controlled character (mob) attacking a player. Therefore, aggro has no relevance in PvP play, but only in PvE.

For example, you may read of a player who died while fighting one mob because she aggroed another mob - that is, another mob decided to attack her because she got too close to it, or for other reasons. See Aggro radius. Aggro is closely associated with the concept of threat. If a mob is under attack by more than one player (or by a player and her pet), then the mob will aggro onto (i.e., will begin to attack) the attacker with the highest threat.

Aggro is understood to be the condition of a particular mob attacking a particular character, while threat is the numeric value that each attacker has towards each character on its threat list. The basic behavior of aggro is controlled by the rules outlined below. Some mobs will have secondary attacks which have different targeting procedures; even for a normal creature, the target who has aggro is not necessarily the player highest on its threat list. Managing aggro is one of the most important aspects of grouping because it determines how much damage the group receives and where the damage ends up.

Holding aggro is done by (usually) one person (the tank) who uses his abilities to make the enemy attack him and no one else. For hunters and warlocks, the pet usually operates as a tank in solo play.

Aggro control is the art and work which is done by all members of a party to force the mob to attack the tank(s).

For a long time it was thought that players would never be able get a sound understanding of how aggro works because it was assumed that it is based on complicated AI algorithms which can't reasonably be deduced from the little information Blizzard has made available to us. Thanks to the work of some dedicated individuals, however, it is now known that this is not the case. Today there is a quite thorough theory on aggro which explains most of the factors involved in a mob's target selection. "