retardation factor, \(R_{\text{F}}\)

in planar chromatography
https://doi.org/10.1351/goldbook.R05353
Ratio of the distance travelled by the centre of the spot to the distance simultaneously travelled by the mobile phase: \[R_{\text{F}}=\frac{b}{a}\] By definition the R F values are always less than unity. They are usually given to two decimal places. In order to simplify this presentation the hRF values may be used: they correspond to the R F values multiplied by 100. Ideally, R F values are identical to the R values used in column chromatography.
Source:
PAC, 1993, 65, 819. 'Nomenclature for chromatography (IUPAC Recommendations 1993)' on page 845 (https://doi.org/10.1351/pac199365040819)