An affirmative defense is a legal strategy used by a defendant in a court case. It involves presenting evidence or arguments that, if proven, can negate or lessen the legal consequences of the defendant's actions, even if the prosecution's claims are true. This means the defendant admits to the act but argues that there are valid reasons or justifications for it. Common examples of affirmative defenses include self-defense, insanity, and duress. By using an affirmative defense, the defendant shifts the focus from merely denying the allegations to providing a legitimate reason for their behavior, which can lead to reduced charges or even acquittal.