horizontal elution (horizontal development)

in planar chromatography
https://doi.org/10.1351/goldbook.H02858
A mode of operation in which the paper or plate is in a horizontal position and the mobile-phase movement along the plane depends on capillary action.
Source:
PAC, 1993, 65, 819. 'Nomenclature for chromatography (IUPAC Recommendations 1993)' on page 829 (https://doi.org/10.1351/pac199365040819)