World of Warcraft, or WoW, is a fantasy online game set in the Warcraft universe. It is known for popularizing the MMOG platform and MMORPGs specifically. Gameplay focuses on questing, Player versus Environment combat, and Player versus Player combat. The game features two opposed factions which players must select and which determine players' ability to communicate with other players. It also features large, extended quests, called raids, which are only completable by large groups of players. It uses the subscription model of payment and has three optional expansions.