black body In physics, an ideal body that absorbs all incident radiation and reflects none. Such a body would look ‘perfectly’ black. Wien's law, Stefan's law, and Planck's law of black body radiation grew out of this study, as did Planck's discoveries in quantum mechanics.

black body A body which absorbs electro-magnetic energy perfectly. If the body remains at constant temperature then it also radiates electromagnetic radiation perfectly in equilibrium with that which it absorbs. See also STEFAN-BOLTZMANN LAW.