An ion which absorbs through coulomb forces only and which is hence only repelled by surfaces of like sign, attracted by surfaces of opposite sign, and is not absorbed on an uncharged surface.
See also: specifically absorbing ion
Source:
PAC, 1991, 63, 895. 'Nomenclature, symbols, definitions and measurements for electrified interfaces in aqueous dispersions of solids (Recommendations 1991)' on page 899 (https://doi.org/10.1351/pac199163060895)