A raid is a type of mission in a video game in which a very large number of people (larger than the normal team size set by the game) attempt to defeat a boss monster. This type of objective is most common in MMORPGs, where the servers are designed to handle the number of users, and usually but not necessarily occurs within an Instance dungeon. In RTS games like StarCraft, the term is used differently; see Raid (military).
Raiding originated in the class of text MUDs known as DikuMUD. DikuMUD heavily influenced the game EverQuest which brought the raiding concept into modern 3D MMORPGs. The largest and most popular game to currently feature raiding is World of Warcraft.
The combat encounters comprising a raid usually require players to coordinate with one another while performing specific roles as members of a team. The roles of Tank, Healers, and DPS are known as the Holy Trinity of MMORPG group composition. Other common roles include Buffing, Crowd control, and Pulling (selectively choosing targets with which to initiate combat). A raid leader is often needed to direct the group efficiently, due to the complexities of keeping many players working well together.
Raids are often very rewarding in terms of virtual treasure and items that are unique or that grant exceptional stats and abilities, thus giving players an incentive to participate. Often however, there is not enough treasure to individually reward every player who participates. Players have invented various systems, such as Dragon kill points to distribute loot fairly.
Raiding is often done by associations of players called guilds or clans who maintain a consistent schedule and roster. There are two types of raiding guilds: casual guilds, defined as spending two to three days per week on average; and hardcore guilds, defined as spending four to seven days per week on average.
The fact that raids often require multiple consecutive hours of constant gameplay leads some to believe it is a physically unhealthy activity. A 2003 study by the National Institutes of Health found that playing MMORPGs for more than 20 hours per week correlates to obesity and nutritional imbalance as well as an increased propensity for bone loss and muscle atrophy. Due to these concerns, China has proposed national limits on how long people can play MMORPGs. The measures will impose penalties on people who play MMORPGs for more than 3 hours per day.