Question

What do you call a situation in which anyone’s gain comes at someone else’s expense

Answer 1

The term for what you are describing is "zero sum", in which one benefits from another's loss.

Answer 2

A situation in which anyone's gain comes at someone else's expense is called a zero-sum situation.

Step-by-step explanation:

Zero-sum is an adjective related to a situation in which whatever is gained by one side is lost by the other. This means that, in any competitive situation, one side can't win unless the other one loses. Zero-sum means that when the losses are subtracted from the gains, the sum is zero.