MAD' MAD is an acronym for 'Mutually Assured Destruction', a term used to describe the Cold War strategy of nuclear deterrence. This strategy was based on the idea that if two opposing sides had enough nuclear weapons to destroy each other, then neither side would be willing to launch a first strike, as it would result in their own destruction. The term 'LEX' is short for lexicon, which is a collection of words and their definitions.