A measure of the amount of light absorbed by a substance suspended in a matrix. The matrix may be gaseous, liquid, or solid in nature. Most biologically active compounds (e.g., proteins) absorb light in the ultraviolet (UV) or visible light portion of the spectrum. Absorbance is used to quantitate (measure) the concentration of the substance in question (e.g., substance dissolved in a liquid).
Ability of a substance to absorb light or X rays. Materials with high absorbance for X rays are termed radiodense or radiopaque.
ln health care, the ability of a material or a tissue to absorb electromagnetic radiation.