1. The ability of a material or tissue to absorb radiation which depends on temperature and wavelength; expressed as the negative common logarithm of the transmittance (ratio of transmitted energy to incident energy): "The new equipment in the laboratory was able to effectively measure the absorbance of the diseased tissue of the patient."
2. A measure of the extent to which a substance transmits light or other electromagnetic radiations: "Absorbance varies with factors: such as, wavelength, solution concentration, and path length."