A Non-Player Character" (NPC) is any character you encounter and interact with in WoW that is not controlled by other human players - they are generated and controlled by the game server.
Typical examples of NPCs include Flight Masters, Quest Givers, Vendors, Trainers, and Guards.
Hostile NPCs are sometimes categorized with other creatures or monsters (aka "Mobs").
Contrast with Player Characters (PCs, or sometimes just "Players").
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