Black body is the ideal concept in physics. One of the significant properties of the black body is whatever heat it absorbs completely emits it.
The emissive power of the black body is maximum and absorptive power of the black body is one.
Stefan, one of the scientist, completely studied about the black body, according to him, the total energy radiated by a black body per unit area of its surface in a unit time is proportional to fourth power of absolute temperature. Boltzmann contributed to this topic by introducing the thermodynamic principles and derive Stefan's law and it is also known as fourth power law.