Русско-англо-русский юридический словарь

In U.S. criminal law, necessity may be either a possible justification or an exculpation for breaking the law. Defendants seeking to rely on this defense argue that they should not be held liable for their actions as a crime because their conduct was necessary to prevent some greater harm and when that conduct is not excused under some other more specific provision of law such as self defense. (Wikipedia)

Necessity: A defense that permits a person to act in a criminal manner when an emergency situation, not of the person's own creation compels the person to act in a criminal manner to avoid greater harm from occurring. (http://nationalparalegal.edu)