Absorbtance
Absorbtance : (Phys; Symb: a or a) The ratio of radiant flux absorbed by a body or material to the radiant flux incident upon it. Also called: Absorption Factor. Note: Absorptance measured over all wavelengths is total absorptance; at a given wavelength it is spectral absorptance; and in the visible range it is referred to as optical absorptance. Cf. attenuation