Aggro

From AionSource.com Wiki

Aggro, sometimes referred to as "Hate," 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. Obviously, 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 on its threat list with the most threat. 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 who uses his abilities to make the enemy attack him and no-one else.

Aggro control is the art and work which is done by all members of a party to allow the enemy to attack a certain agreed person.

In the Context of Aion

According to a video of an Aion GC2008 presentation, when not engaged in battle, higher level players do not attract the aggression of nearby mobs. However, it is unclear how this works.