The thermal radiation that would be emitted by a black body. Black-body radiation has a characteristic spectrum, described by Planck’s law, in which the peak of the emission moves to shorter wavelengths as the temperature of the black body rises (see Wien’s Displacement Law). The cosmic background radiation is black-body radiation, and stars often act as black-body radiators in the optical part of the spectrum.

black-body radiation:

The higher the temperature of a black body, the more the peak of the emitted radiation is displaced towards shorter wavelengths. Hot stars have a peak in the ultraviolet, while cool stars peak in the infrared. Solar-type stars have a peak in the visible part of the spectrum.