Asymmetry of a peak such that, relative to the baseline, the front is less steep than the rear.
In paper
chromatography and
thin-layer chromatography, it refers to the distortion of a spot showing a diffuse region in front of the spot
in the direction of flow.
Source:
PAC, 1993, 65, 819
(Nomenclature for chromatography (IUPAC Recommendations 1993))
on page 837