A barefaced tenon is a tenon with only one shoulder.
Right:Where a rail is thinner than its stile, a barefaced tenon allows the rail's face to be set below the stile's.
One such use might be in making a frame that will be filled with stable material such as plywood or MDF.
One snag is that in having only one shoulder, the job is likely to cramp-up out of alignment, ie the plane of the rail would not be parallel with the plane of the stile.
Left:A Barefaced tenon on a slender rail of a bookrack's.
The overhang allows the top of the rail to end flush with the outer face of the rack.
When driving home the wedges, tap them in at an equal rate or you will find that you have tightly closed one saw cut.