Nash equilibrium is an important equilibrium or solution concept in non-cooperative game theory. A Nash equilibrium is a strategy profile (i.e. a strategy for each player) in which each player is playing a best response to the strategy of the other(s). More simply, a Nash equilibrium describes a situation in which each person acts optimally given the actions of the others, so that no one wants to change his or her action.

The net present value (NPV) is used in finance and economics to describe or measure today´s value of a stream of future payoffs or payments. Many decisions that we take will not only have immediate (financial) consequences, but will also lead to future expenses or revenues. For example, if you take out a loan or a mortgage you receive a one-time payment today from your bank and in return you will have to pay back the loan plus interest in monthly installments. An insurance company will receive monthly contributions from their clients but has to pay in case of an accident.