The horizontal members of a face frame are called rails and the vertical pieces are called stiles. Usually they are 1 1/2" wide, cover the front edges of the box, and are made of solid wood. Some cheap framed cabinets have a vertical divider where the doors meet in a double door cabinet. Everybody dislikes them because the stile prevents full cabinet access. If you see a center stile on a cabinet 36" wide or less, it's an indicator of poor quality. In cabinets wider than 36" the center stile is needed even in good quality cabinets to help keep the frame square.