In jurisprudence, duress or coercion refers to a situation whereby a person performs an act as a result of violence, threat or other pressure against the person. Black's Law Dictionary (6th ed.) defines duress as "any unlawful threat or coercion used... to induce another to act [or not act] in a manner [they] otherwise would not [or would]". Duress is pressure exerted upon a person to coerce that person to perform an act that he or she ordinarily would not perform. The notion of duress must be distinguished both from undue influence in the civil law and from necessity.

Duress has two aspects. One is that it negates the person's consent to an act, such as sexual activity or the entering into a contract; or, secondly, as a possible legal defense or justification to an otherwise unlawful act. A defendant utilizing the duress defense admits to breaking the law, but claims that he/she is not liable because, even though the act broke the law, it was only performed because of extreme unlawful pressure. In criminal law, a duress defense is similar to a plea of guilty, admitting partial culpability, so that if the defense is not accepted then the criminal act is admitted.