interface

The plane ideally marking the boundary between two phases.
Note:
The term should not be used synonymously with interphase.
Source:
PAC, 1986, 58, 437 (Interphases in systems of conducting phases (Recommendations 1985)) on page 439
See also:
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
Orange Book, p. 251