Extinction coefficient ( E)
The term "extinction coefficient" with the symbol E is an alternative term for "molar absorption coefficient."
The use of this older term is no longer recommended for absorbance or specific absorbance.
Other similar definitions are the "molar absorption coefficient, molar extinction coefficient, or molar absorptivity (ε)."
It measures how strongly a molecular species absorbs light at a given wavelength.
The absorbance of light at a given wavelength of a substance is dependent on the mass density or molar concentration of the specific substance.