The velocity of a charged analyte under the influence of an electric field relative to the background electrolyte. Also called rate of migration (in electrophoresis).
Source:
PAC, 2004, 76, 443. 'Terminology for analytical capillary electromigration techniques (IUPAC Recommendations 2003)' on page 448 (https://doi.org/10.1351/pac200476020443)