In physics, a black body is any body capable of completely absorbing all the incident electromagnetic radiation on its surface.
There is no such body in nature having the required properties, but in the laboratory models can be built which, under certain conditions, can accurately simulate the behaviour. Any isothermal enclosure, sealed except for a very small aperture, acts as a black body.
Black bodies, like all other bodies, emit radiation in a characteristic spectrum which depends exclusively on the absolute temperature. For each temperature value there is a dominant wavelength.