"Zero-sum" describes a situation in which a one person's gain is exactly balanced by losses of the other participant(s).This situation exists whenevery the total amount of resources to be won is fixed. For example:
- votes in an election.
- global supplies of fresh water
- chips in a poker game
- customers in a mature market for a product like cola.
- Cutting a birthday cake.
- distributing tax revenues
These are all situations where cooperation between competitors is unlikely, and the competition can get nasty in a way that is mutually destructive.
A non-zero sum game is a situations where participants can all gain or suffer together, such as a country with an excess of bananas trading with another country for their excess of apples, where both benefit from the transaction.
game theory - wikipedia