A substance which lowers the
surface tension of the medium in which it is dissolved, and/or the
interfacial tension with other phases, and, accordingly, is positively adsorbed at the liquid/vapour
and/or at other interfaces.
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 611