Dominant strategy

A strategy that gives a player at least as high a payoff as every alternative, for every possible combination of other players’ choices.

Strict dominance: A strategy is strictly dominant when it gives a player a higher payoff than every alternative in every case. This stronger form guarantees a strict gain regardless of others’ choices.
Prisoner's dilemma: A game in which individually rational choices produce a worse outcome for both players than mutual cooperation. Defection is dominant for each prisoner, despite the jointly better cooperative outcome.
Dominated strategy: A strategy that yields a lower payoff than another strategy for every possible choice by the other players. Dominance identifies strategies that can be discarded, the reverse comparison from a dominant strategy.
Normal-form game: A representation of a strategic interaction specifying players, their strategies, and the payoffs for each strategy profile. Dominance is defined by comparing a player's strategies within this game representation.
Weak dominance: A strategy weakly dominates another when it never gives a lower payoff and gives a higher payoff in at least one case. Dominant strategies may tie with alternatives in some cases rather than always outperform them.
Truthful bidding: Submitting a bid equal to one's true valuation of an item. In a Vickrey auction, bidding truthfully is a dominant strategy for each bidder.
Maximin strategy: A strategy that maximizes a player's worst possible payoff across the other players’ choices. Maximin focuses on the worst case, while dominance compares payoffs in every case.
Strategy (game theory): A complete plan specifying a player's action for every situation the game may reach. A dominant strategy is a strategy judged against all alternatives in the player's strategy set.
Payoff matrix: A table that lists each player's payoff for every combination of strategies. Comparing a player's entries across opponents’ choices reveals whether a strategy dominates.
Vickrey auction: A sealed-bid auction in which the highest bidder wins but pays the second-highest bid. Its payment rule makes truthful bidding dominant under standard assumptions.

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