The Ultimatum Game is an experimental game in game theory where two players interact and have to decide how to divide a sum of money. One player, called the "proposer," is given a sum of money and must propose a way to divide it between themselves and the other player, called the "responder." The responder can either accept or reject the proposal.
If the responder accepts the proposal, the money is divided according to the proposal. However, if the responder rejects the proposal, neither player receives any money. The game is interesting because it is often assumed that people are rational and self-interested, so the responder should accept any offer greater than zero. However, in practice, responders often reject proposals that they perceive as unfair. This behavior has been observed across many different cultures and contexts, and it has been argued that it reflects a concern for fairness or reciprocity in human decision-making.