Non-Player Character
From AmtWiki
In a traditional role-playing game such as Dungeons & Dragons, an NPC is controlled by the gamemaster. Non-player characters populate the fictional world of the game, and can fill any role not occupied by a player character (PC). Non-player characters might be allies, bystanders or competitors to the PCs.
NPCs vary greatly in importance, from the NPC innkeeper seen once by the player characters, to the NPC arch-nemesis who comes back time-and-again for an entire campaign. In Amtgard NPCs are typically Monsters or guides in Quests.