1) Included between two faces 2) Surface 
• (a.) Included between two plane surfaces or faces; as, an interfacial angle.
In`ter·fa'cial adjective (Geom.) Included between two plane surfaces or faces; as, an interfacial angle. 
Type: Term Pronunciation: in′tĕr-fā′shăl Definitions: 1. Relating to an interface.
[adj] - relating to or situated at an interface
adjective relating to or situated at an interface; `an interfacial layer`; `interfacial tension is the surface tension at the interface between two liquids`
included between two faces. · of, pertaining to, or of the nature of an interface.