MDF is Minimum Defense Frequency, the lowest percentage of hands you must defend to prevent exploitation.
Explanation. Derived from game theory, MDF defines the minimum frequency you must call or 3‑bet against bets to avoid giving profit to your opponent. For instance, if facing a 50% pot c‑bet, MDF ≈ 33%. Playing under MDF yields opponent bluffs profitable; playing over allows bluff-catching. It’s core to balanced strategy.