A situation in which a gain by one person or side must be matched by a loss by another person or side: “It's not a zero-sum game in which either youth or pensioners must lose” (Earl W. Foell).
(plural zero-sum games)
zero-sum game - Investment & Finance Definition
A trading situation in which profits are limited and wealth is merely shifted around. The futures and options markets are zero-sum games because for every trader who makes money, another trader loses money.