absorption pathlength

of a sample cell
The length of the radiation path through the absorbing medium; it is equal to the cell path length, l, in the case of single-pass cells at normal incidence of radiation.
PAC, 1988, 60, 1449. 'Nomenclature, symbols, units and their usage in spectrochemical analysis - VII. Molecular absorption spectroscopy, ultraviolet and visible (UV/VIS) (Recommendations 1988)' on page 1453 (https://doi.org/10.1351/pac198860091449)