In game theory a positive-sum game is one in which players, as a whole, end up with more benefit after playing than they started with. 'Game', in this case, simply means an interaction, including anything from a conversation to a peace treaty. Most games are positive-sum, as those are the ones that people seek out and attempt to engage in frequently.
There are various definitions of 'positive-sum', which can lead to significantly different judgments. The most common definition is simply: "the sum of winnings and losses is greater than zero." In this case, if you throw a party and everyone but Bob has a wonderful time, you initiated a positive-sum game.
Another common definition is: "no one wins at someone else's expense, and the positives outweigh the negatives." In this case, throwing a party in which we all mock Bob would not count as positive-sum.
This distinction is primarily a matter of focus. The first definition is determining if a case is positive-sum for the group; the second for the individual(s). In most large-scale real world games there is no hope of meeting the second definition. There is no political or economic decision that benefits everyone, almost by definition; if it benefits everyone, it is not a political or economic concern, it's just this thing we do.
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