Party cohesion

party cohesion, n. in RPGs, the ability of the player characters in a party (and often, the players in a game) to cooperate constructively and avoid competition and in-fighting.
Ex: Player 1: "While Sir Goodalot is asleep, I'm going to pick his pockets." Player 2: "Dammit, Jerry, if you don't stop fucking with the party cohesion, my dwarf is gonna kick your ass!" Player 1: "That's not fair! Your dwarf doesn't know what my thief is doing!" [GJ1]
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Addendum: Party cohesion is important in a game, both IC and OOC. With Role-playing as a highly social experience, it is imperative that everyone is able to get along at the table, or else the game itself will bog down with constant fights, attempts at revenge through metagaming where enemy players screw eachother over, or just plain refuse to cooperate. In character party cohesion is more necessary with players who are still new to one another, so they don't end up taking things personally. In character cohesion becomes less and less important as the experience level and maturity of the gaming group increases; from there having PCs that are all but blood enemies forced into working together while secretly working to tweak one anothers' goals can lead to some interesting drama, as long as the GM can keep the plot moving.