Interface

A surface or region separating two different materials or media (solids, liquids, gases, or combinations) across which mechanical, thermal, electrical, or chemical properties are discontinuous or change rapidly; a locus where boundary conditions are applied and interfacial phenomena occur.

The contact surface or zone where two materials, systems, or formal elements interact and exchange forces, information, energy, or effects; the designed properties of that zone determine compatibility, communication, and performance across the junction.