1. Attaching boards to framing or sheathing with nails driven through the edge of each piece so as to be concealed by the succeeding board. 2. In installing tongue-and-groove flooring, the nails are placed at the root of the tongue where they will be hidden by the groove of the next piece; the nails pierce the subfloor at a 45 degree angle. 3. The practice of nailing the back portion of a roofing ply so that the nails will be concealed by the next ply of roofing.