in freeze fracture the plasma membrane cleaves between the acyl tails of membrane phospholipids, leaving a monolayer on each half of the specimen. The e face is the inner face of the outer lipid monolayer. From within the cell this is the view that you would have of the outer half of the plasma membrane if the inner layer could be removed. The complementary surface is the p face (the inner surface of the inner leaflet of the bilayer). E stands for ectoplasmic, P for protoplasmic: not terms that are in common usage!