For monochromatic radiation, absorbance (A) is determined by the relationship: A = abc, with a = absorptivity, b = path length through the medium, and c = concentration of the absorbing species. The intensity of a ray of light which has gone through a medium.
[Fundamentals of Analytical Chemistry; Skoog, Douglas A.; West, Donald M.; Holler, James F.; Ed. Jennifer Bortel; p. 510; 1996; Saunders College Publishing; Fort Worth, Texas.] [The Gulf Publishing Company Dictionary of Business and Science; Tver, David F.; p. 58; 1974; Gulf Publishing Company; Houston, Texas.]
Source: Atmospheric Chemistry Glossary