rate of migration, v

in electrophoresis
https://doi.org/10.1351/goldbook.R05154
The distance of migration divided by time, sometimes called velocity of migration. The symbol v is also used for velocity.
Source:
PAC, 1994, 66, 891. (Quantities and units for electrophoresis in the clinical laboratory (IUPAC Recommendations 1994)) on page 895 [Terms] [Paper]