Hobbies And Interests
Definition
In general, the term "aggro" indicates having the attention of one or more enemies. For example, if a player were to say "I almost killed that elite, but then I got aggro from two more enemies," he means that two more enemies noticed him and joined the fight partway through. The term also serves as a verb: For example, "I'm sorry about that, my pet aggroed the boss," means that the player's pet accidentally attracted the attention of the boss.
Threat
The concept of threat is closely linked to aggro. Every action performed during a fight, whether it consists of damaging an enemy directly or healing other players, generates a specific amount of threat toward the enemies involved in the fight. Each enemy, while in combat, has a threat list -- a list of all the players who have performed threat-generating actions ordered by the total amount of threat generated. The player at the top of the threat list is the one who has aggro.
The term "aggro" is also occasionally used interchangeably with "threat." For example, a player might say "Let me build some aggro before you start attacking," meaning that other players should wait until he has generated enough threat on the enemy to make it unlikely that other players will overtake him on the list.
Group Roles
Knowing how threat and aggro work is important when participating in group play. Players who take on the role of tank -- the member who takes damage in a party -- specialize in holding aggro, keeping an enemy's attention, and building threat to remain at the top of the threat list and prevent the enemy from turning to other players. Tank characters typically do not deal much damage, but have high health and defenses, allowing them to withstand multiple hits from powerful enemies without dying. Conversely, players who take on the role of damage dealer aim to deal as much damage to the enemies as possible while remaining below the tank on the threat list. Getting aggro is usually disastrous for a damage dealer, due to this type of character having lower health and defenses.
Considerations
Certain fights, especially in raid content, may have more complex threat or aggro mechanics. For example, Voracious Hatchlings that appear during the Alysrazor fight in the Firelands raid will focus on whoever is closest to them when they first appear and won't switch targets unless the player they are focusing on dies, regardless of threat generated. Void Reaver, a boss in the Tempest Keep raid, will periodically knock away the player at the top of its threat list and reduce her threat, eventually forcing another player to the top of its threat list.