Mixed strategy
Randomizing your moves so opponents can't predict you.
What it means
A strategy in which a player chooses among their possible actions according to a probability distribution rather than committing to one pure action. Mixing is essential in games with no pure-strategy equilibrium, where any predictable choice can be exploited, so the player randomizes to keep opponents indifferent and unable to gain by anticipating them. Nash proved that every finite game has at least one equilibrium once mixed strategies are allowed, securing the generality of his concept. It matters in competitive settings from poker bluffing to penalty kicks to tax audits, where unpredictability itself is the optimal policy.
Examples
A soccer player taking penalties varies kicking left or right at random so the keeper can't lean the correct way.
A tax authority audits a random share of returns instead of a fixed list of professions; if filers could work out who gets checked, everyone else would understate freely.
A poker player who only raises with strong hands is read for free, so she bluffs on a set fraction of weak ones — the randomness, not the bluff, is what pays.
First described in Game theory; Nash (1950); von Neumann.