Active defense is a term used in military strategy to describe the action of defending strategic positions by taking aggressive measures against the enemy. There are various synonyms for active defense, including aggressive defense, offensive defense, and dynamic defense. Aggressive defense implies using forceful tactics to protect an area or target, while offensive defense involves preemptive strikes before an attack occurs. On the other hand, dynamic defense suggests proactive measures to maintain a fluid front line or to take advantage of enemy weaknesses. Ultimately, the choice of which defense strategy to use will depend on the specific circumstances of the situation, including the landscape, the strength of the opposing forces, and the nature of the threat.