Blackbody is the term in physics that stands for imaginary physical body that absorbs 100% of light/electromagnetic radiation. In reality blackbody is just an idea, hypothetic object. I does not exist and the closest material with that property in our universe was created in 2014 and called Vantablack (carbon nanotube array). It absorbs 99,965% of all electromagnetic radiation. However, the notion of a blackbody is still useful and often used in physics to test theories and prove our knowledge of the world. Obviously, if a blackbody absorbs radiation, it has to emit the same volume of radiation too. Otherwise, only acquiring energy without giving it away, the blackbody will inevitably explode.
The 1904 Nobel prize winner and British scientist, Lord Rayleigh, and his fellow scientist, Sir Jeans, derived the law that governs the blackbody energy emission dependency of the wavelength of the radiation absorbed.