Crowd control (also called CC) is a term used in massive multiplayer online role-playing games (MMORPG)s to refer to the ability to limit the number of mobs actively fighting during an encounter. It can also refer to abilities that influence or prevent the abilities or actions of other character(s). Crowd control can be extremely powerful, controlling the possible outcomes of an encounter, as it forces opponents to use a smaller set of abilities/actions. Players use crowd control to create offense/defense ratio imbalances between themselves and their opponent(s); used properly, CC often renders an opponent nearly useless, allowing the CCer to use abilities/actions against an opponent without fear of retaliation or response. In a group setting, crowd control often makes combat safer, easier, or viable.

Definition: When used online, especially while playing an MMORPG, this term is used to describe a player character class which is designed to absorb damage from others or computer aided characters.

"Tank" characters are especially important in large group instances. A Tank's job is to stand before the group, using their abilities and high armor values to force a particular "mob" (or group of) to continue attacking the Tank, while other characters contribute to over all damage while not taking damage themselves.

Aggro is understood to be the condition of a particular mob attacking a particular character. 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.