1) Absorption coefficient 2) Coefficient 3) Coefficient of absorption 4) Physical quantity 
The ratio of the luminous or radiant flux absorbed by a body to the flux falling on it. Absorptance is generally represented by the Greek letter a (alpha). By definition, in the case of a blackbody a = 1. Absorptance was formerly known as absorptivity.
ratio of the absorbed radiant or luminous flux to the incident flux under specified conditions unit: 1
The dissipation of light (radiation) within a surface or medium, caused by the conversion of radiant (luminous) energy to a different form of energy, usually heat, by interaction with matter. The absorption is the "missing piece", when comparing the total reflected and transmitted energy with the incident energy. The ratio of the total absorbed rad...
The ratio of solar energy absorbed by a surface to the solar energy striking it.
the ratio of the amount of radiation absorbed by a surface to the amount of radiation incident upon it. Cf. reflectance, transmittance (def. 2).