A defense based on facts other than those that support the plaintiff's or government's claim. A successful affirmative defense excuses the defendant from civil or criminal liability, wholly or partly, even if all of the allegations in the complaint are true.
Examples of affirmative defenses include:
Contributory negligence, which reduces a defendant's civil liability when the plaintiff's own negligence contributed to her injuries.
Statute of limitations, which prevents a party from prosecuting a claim after the limitations period has expired.
Self defense, which excuses a defendant's criminal culpability.