A concept of an idealized surface has been made which are perfect emitter and absorber of radiation. This ideal surface is known as a black body.
A black body or ideal radiator is a body that emits and absorbs at any temperature the maximum possible radiation at any given wavelength.
A black body has the following features
At a specified temperature and wavelength a black body emits more radiation energy than the real one.
It absorbs all incident radiation regardless of wavelength and direction
It emits radiation energy uniformly in all direction. That is black body is a diffuse emitter the term ‘diffuse’ means independent of direction.