A faction is a group of allies, either racial or ideological. Most in-game factions are described in Warcraft lore, while others have been introduced in World of Warcraft. The two playable factions are Alliance and Horde.
Most factions are tracked in World of Warcraft by the reputation a character has with each faction. Some groups that are not tracked as factions appear in the organization list.
In World of Warcraft, a character's main faction is chosen based on the race they pick. Alliance races include Night Elves, Dwarves, Gnomes, Humans, Draenei, and Worgen. Horde races include Trolls, Orcs, Tauren, the Forsaken, Blood Elves, and Goblins.
Each joinable race has a starting zone, and most have a city where players can gather, find vendors, trainers, and other facilities. Both factions have major cities where players gather: the Alliance in Stormwind, and the Horde in Orgrimmar.