absorption coefficient

https://doi.org/10.1351/goldbook.A00037
Linear decadic (a,K) and Napierian absorption coefficients (α) are equal to the corresponding absorbances divided by the optical path length through the sample. The molar absorption coefficients (decadic ɛ, Napierian κ) are the linear absorption coefficients divided by the amount concentration.
Source:
Green Book, 2nd ed., p. 32 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)