Zero-sum describes something, such as a game, mentality, or situation, in which any gain corresponds directly with an equivalent loss.

// Dividing up the budget is a zero-sum game.

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“Domestic migration is zero-sum, meaning a loss of college graduates prized by local officials and tax collectors in Washington or San Francisco can be a gain for Kansas City or Orlando.” — Josh Katz, The New York Times, 15 May 2023

Does game theory sound like fun? It can be—if you are a mathematician or economist who needs to analyze a competitive situation in which the outcome is determined by the choices of the players and chance. Game theory was introduced by mathematician John von Neumann and economist Oskar Morgenstern in their 1944 book The Theory of Games and Economic Behavior. In game theory, a zero-sum game is one, such as chess or checkers, where each player has a clear purpose that is completely opposed to that of the opponent. In economics, a situation is zero-sum if the gains of one party are exactly balanced by the losses of another and no net gain or loss is created; however, such situations in real life are rare.