Question

what is concept of black body radiation?

Answer 1

absorbing all electromagnetic radiation...

Answer 2

that would be a black body itself. Here is wikipedia's definition of black body radiation:
The thermal radiation from a black body is energy converted electrodynamically from the body's pool of internal thermal energy at any temperature greater than absolute zero. It is called blackbody radiation and has a frequency distribution with a characteristic frequency of maximum radiative power that shifts to higher frequencies with increasing temperature.
http://en.wikipedia.org/wiki/Black_body