header (framing)

1. A horizontal structural member that supports the load over an opening, for example a window or a door, and is supported on each end by a trimmer stud. 2. One or more pieces of lumber installed around openings in walls, floor, ceiling, and roof framing to support free ends of studs, floor joists, ceiling joists, and rafters, and to transfer their load to other parallel framing members. 3. A structural member installed at right angles to the majority of framing members in a wall, floor or roof. 4. A member nailed on the ends of joists and resting on a wall plate or sill plate; also called a Box Sill.