Critical Nuclear Weapon Design Information

Critical Nuclear Weapon Design Information (CNWDI, often pronounced SIN-widdy or SIN-wuh-dee) is a U.S. Department of Defense (DoD) category of Top Secret Restricted Data or Secret Restricted Data that reveals the theory of operation or design of the components of a thermonuclear or fission bomb, warhead, demolition munition, or test device. Specifically excluded is information concerning arming, fuzing, and firing systems; limited life components; and total contained quantities of fissionable, fusionable, and high explosive materials by type.

Source: Wikipedia — Critical Nuclear Weapon Design Information (CC BY-SA 4.0)