The radiation emitted by a body as a result of its temperature (i.e., thermal motion of its electrons). In general, the thermal radiation emitted by a body depends to some degree on the composition of the body, but for a special class of radiators known as blackbodies, the radiation, known as blackbody radiation, always follows the same law (i.e., the Planck law).
References
Eisberg, R. and Resnick, R. "Thermal Radiation." §1-2 in Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles, 2nd ed. New York: Wiley, pp. 2-6, 1985.
