Black body

A black body is something that looks completely black, but it actually emits radiation in all directions (including light, although you can't see the light that it emits). The radiation that it emits is related to the temperature of the black body; if it is cooler, it will emit less radiation, and if it is warmer, it will emit more radiation. Black bodies absorb all the radiation that falls onto them and will eventually reach a temperature where it no longer absorbs radiation but emits it in all directions. That is why they look black - they absorb all the visible light that falls onto them.