PvP

From The StarCraft 2 Wiki

PvP, or Player versus Player game style means that the primary opposition for a player in the game is other players. In the world of MMOs, the opposite of PvP is "PvE", Player versus Environment. For StarCraft, terms like co-op are used instead.

PvP can also refer to a match between two Protoss players, where 'PvP' is instead a match abbreviation.