A sheet of wood held in a frame. 2. The space within the web of a truss between any two panel points on a chord and a corresponding pair of joints or a single joint on an opposite chord. 3. A board on which are mounted the switches, fuses, and circuit breakers for controlling and protecting a number of similar branch circuits, installed in a cabinet and accessible from the front only. Also called panelboard. 4. A distinct section or division of a wall, ceiling, or door, recessed below or raised above the general level or enclosed by a frame. 5. A portion of a reinforced concrete slab bounded on all sides by the centerlines of columns, beams, or walls. 6. A prefabricated section of a floor, wall, ceiling, or roof, handled as a single unit in the assembly and erection of a building.