Absorptivity

The term absorptivity has two meanings:

• In chemistry, it usually refers to Molar absorptivity : the constant $\epsilon$ used in the Beer-Lambert law, $A=\epsilon c l$, where A is the absorbance, c is the concentration of the solution, and l is the path length.
• In physics, the word is used interchangeably with absorbance : the fraction of radiation absorbed at a given wavelength.