Indicated by Gr or Gel if the repulsion is due to electric effects (gr or gel is taken for unit area of each of two flat and parallel surfaces). Gr (or Gel) is defined as \[G_{\text{r}}\,\text{(}\text{or}\,G_{\text{el}}\text{)} = \left[\int _{\text{final distance}}^{\infty }\text{Force} \;\text{d (distance)}\right]_{T,p}\]
Source:
PAC, 1972, 31, 577. 'Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry' on page 615 (https://doi.org/10.1351/pac197231040577)