The 'physics package' is an obfuscated shorthand term used by technicians and designers (at least, in the United States) in the field of Nuclear Weapons, Care and Feeding Thereof to describe the 'nuclear' component(s) of an atomic bomb. This is opposed to, for example, the conventional explosive detonator, or any form of guidance/fusing mechanism. Although usually it refers to that minimum of components needed to form an atomic detonation (as opposed to a conventional one) it is sometimes used by military personnel to refer to an entire functioning nuclear weapon. This is especially true if the weapon is enclosed within or attached to a delivery vehicle such as an ALCM or ICBM RV warhead bus. In this case, 'physics package' might be synonymous with 'warhead'.