What is the common-law defense called when a crime is committed due to a threat of death or serious injury?

The correct terminology for the common-law defense applicable when a crime is committed as a result of a threat of death or serious injury is known as "duress by threats." This defense reflects the principle that if an individual is forced to commit a crime under the immediate threat of harm to themselves or a third party, their culpability may be diminished due to the coercive circumstances they faced.

Duress by threats requires that the threat must be immediate and serious, typically involving life-threatening or significant physical harm. The individual must have acted because they reasonably believed that they had no other choice to avoid the threatened harm, thereby acting under compulsion rather than of their own free will.

The other options provided are different legal concepts. The necessity defense relates to situations where a crime is committed to prevent a greater harm, differing fundamentally from duress, which involves being threatened into committing the act. Intoxication refers to being under the influence of drugs or alcohol, which can affect one’s mental state but does not directly relate to being compelled by a threat. Insanity is a legal defense where a defendant argues that they were not in a sound mental state to understand the nature of their actions, thus focusing on mental health rather than coercion.