What is "mutual assured destruction"

n. (context politics public policy military English) The threat of massive retaliation using nuclear weapons should a potential enemy use them first, both sides being annihilated in the event of war.

Mutual assured destruction or mutually assured destruction (MAD) is a doctrine of military strategy and national security policy in which a full-scale use of nuclear weapons by two or more opposing sides would cause the complete annihilation of both the attacker and the defender (see pre-emptive nuclear strike and second strike). It is based on the theory of deterrence, which holds that the threat of using strong weapons against the enemy prevents the enemy's use of those same weapons. The strategy is a form of Nash equilibrium in which, once armed, neither side has any incentive to initiate a conflict or to disarm.