The failure to do something which a reasonable person would do in a particular situation, or doing something which a reasonable and prudent person would not do in similar circumstances. If an injured person proves that another person acted negligently and caused their injury, they can recover damages to compensate for their injury.

The rule of law under which an act or omission of a claimant is a contributing cause of injury and possible bar to a complete recovery. It can be used as a defence to prevent a claimant from being awarded full damages if he or she did not take reasonable care of his or her self. In the United States, it is a defence that prevents a claimant from being awarded damages if he or she has knowingly and voluntarily accepted the risk of loss, injury or damage.