Player vs. Player: To attack another player while they're trying to fight a monster.
Game Master. GM’s are characters in an MMORPG who are used by employees of the game’s creator company. They monitor the actions of the game world and answer the questions and complaints of the players. They have absolute control and power within the game. If the crime (breaking a law of the game, not the real world) committed is serious enough, they could even expel players permanently from the game.
A person who purposely tries to annoy or anger other players.
Semi-permanent player groups. In typical games, players must use a substantial amount of capital to start the guild.