specific surface area

in surface chemistry
When the area of the interface between two phases is proportional to the mass of one of the phases (e.g. for a solid adsorbent, for an emulsion or for an aerosol ), the specific surface area (a,s or preferably a s) is defined as the surface area divided by the mass of the relevant phase.
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 583
Green Book, 2nd ed., p. 63