A solver is a computational tool using algorithms like Counterfactual Regret Minimization to calculate near-equilibrium poker strategies through millions of simulated iterations. Modern solvers like PioSOLVER, GTO+, and Simple Postflop allow users to configure custom ranges, bet sizings, and decision tree structures. Solver study has revolutionized professional poker by revealing optimal bluff, value, and check frequencies that often contradict conventional wisdom. Understanding solver outputs requires interpreting mixed strategies and translating theoretical frequencies into practical table decisions.