An ideal emitter which radiates energy at the maximum possible rate per unit area at each wavelength for any given temperature. A black body also absorbs all the radiant energy in the near visible spectrum incident upon it.
Also known as a Perfect Radiator.
No actual substance behaves as a true black body, although platinum black and other soots rather closely approximate this ideal. However, one does speak of a black body with respect to a particular wavelength interval. This concept is fundamental to all the radiation laws, and is to be compared with the similarly idealized concepts of the white body and the gray body. In accordance with the Kirchhoff law, a black body not only absorbs all wavelengths, but emits at all wavelengths and does so with maximum possible intensity for any given temperature.
A laboratory device which simulates the characteristics of a black body is known a hohlraum.