A strategy for one player in a game which gives a payoff at least as high for them as any other strategy, regardless of the strategy their opponents adopt. If a player has a dominant strategy, then the player will choose to play this strategy. More generally, if strategy A dominates strategy B there is no point in using B, so strategy B can be eliminated as a potential equilibrium strategy. The search for the equilibrium of a game can be simplified by recursively eliminating dominated strategies.
Reference: Oxford Press Dictonary of Economics, 5th edt.