molar absorption coefficient, ɛ

https://dx.doi.org/10.1351/goldbook.M03972
Absorbance divided by the absorption pathlength, l, and the amount concentration, c:
ɛ λ = 1 c l lg ( P λ 0 P λ ) = A λ c l
where P λ 0 and P λ are, respectively, the incident and transmitted spectral radiant power.
Notes:
  1. The term molar absorptivity for molar absorption coefficient should be avoided.
  2. In common usage for l / cm and c / mol dm −3 (M), ɛ λ results in dm 3 mol −1 cm −1 (M −1 cm −1, the most commonly used unit), which equals 0.1 m 2 mol −1 (coherent SI units).
Source:
PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 371