Strategy (Greek "στρατηγία"—stratēgia, "art of troop leader; office of general, command, generalship"[1]) is a high level plan to achieve one or more goals under conditions of uncertainty.
In game theory, a strategy refers to the rules that a player uses to choose between the available actionable options. Every player in a non-trivial game has a set of possible strategies to use when choosing what moves to make.
A strategy may recursively look ahead and consider what actions can happen in each contingent state of the game—e.g. if the player takes action 1, then that presents the opponent with a certain situation, which might be good or bad, whereas if the player takes action 2 then the opponents will be presented with a different situation, and in each case the choices they make will determine our own future situation.
Strategies in game theory may be random (mixed) or deterministic (pure). Pure strategies can be thought of as a special case of mixed strategies, in which only probabilities 0 or 1 are assigned to actions.
Strategy based games generally require a player to think through a sequence of solutions to determine the best way to defeat the opponent.