Affirmative defense

A defense in which the defendant introduces evidence, which, if found to be credible, will negate criminal or civil liability, even if it is proven that the defendant committed the alleged acts. Self-defense, entrapment, insanity, and necessity are some examples of affirmative defenses. See, e.g. Beach v. Ocwen Fed. Bank, 523 U.S. 410 (1998).