Definitions for "Nash equilibrium"
An equilibrium in game theory in which each player's action is optimal given the actions of the other players. E.g., in a tariff-and-retaliation game, with each country able to improve its terms of trade with a tariff, zero tariffs are not Nash, since each can do better by raising its tariff. A Nash equilibrium, with positive tariffs, is likely to be inferior to free trade for both.
In game theory, a situation in which no player has an incentive to change their strategy.... more on: Nash equilibrium
(game theory) a stable state of a system that involves several interacting participants in which no participant can gain by a change of strategy as long as all the other participants remain unchanged