At an electrified interface, the locus of the electrical centres of non-specifically adsorbed ions in their position of closest approach.
Source:
PAC, 1991, 63, 895. 'Nomenclature, symbols, definitions and measurements for electrified interfaces in aqueous dispersions of solids (Recommendations 1991)' on page 900 (https://doi.org/10.1351/pac199163060895)