An ideal emitter which radiates energy at the maximum possible rate per unit area at each wavelength for any given temperature. A blackbody also absorbs all the radiant energy incident on it; i.e., no energy is reflected or transmitted.
nbsp;NASA Earth Observatory

A hypothetical object that absorbs all of the radiation that strikes it. It also emits radiation at a maximum rate for its given temperature.
WRCC Climate and Weather Terms Glossary