In legal terms, what is an affirmative defense?

An affirmative defense is one that acknowledges the defendant's involvement in the act or behavior that led to the legal action but provides a justification or excuse for that conduct. This means that the defendant admits to the behavior but also presents evidence or a rationale that may lead the court to absolve them of liability or reduce their culpability. Common examples include self-defense in criminal cases or necessity in tort cases.

This understanding distinguishes affirmative defenses from claims that entirely negate liability, such as those that assert the defendant did not perform the action in question. While a counterclaim is a different legal assertion made by the defendant against the plaintiff, it does not fit the specific definition of an affirmative defense. Similarly, a plea for leniency based on circumstances does not justify the act itself but rather seeks a softer punishment, which is beyond the framework of what constitutes an affirmative defense.