Obviously, the opposite of a zero-sum game
. This means that the total amount of money
, whatever resource
the game is about) is not constant. Thus, there can be game situations where all parties gain, or ones where all parties lose, as well as any mix inbetween.
Generally, non-zero-sum games tend to be more interesting and realistic than zero-sum ones, because they can reward lasting cooperation between players, not just alliances that last until they manage to defeat all their enemies, at which point the members of the alliance turn upon each other.
The typical example of a non-zero-sum game in game theory is the Prisoner's Dilemma.
A real-life example is world politics, because a war typically ends up with everybody involved losing, compared to a peaceful situation.