A pair of faces in a solid that share an edge.
Example
In the figure below, the crosshatched face ABCD and the grey face ABEF are adjacent faces, and they share a common side \(\overline{\textrm{AB}}\).
In the figure below, the crosshatched face ABCD and the grey face ABEF are adjacent faces, and they share a common side \(\overline{\textrm{AB}}\).