1. The rear, reverse, unseen, more remote, or less important part of a structure, tool, or object.
2. The support for a more prominent or visible element; e.g., the back of wallboard is the surface to be plastered.
3. The top or exposed side of a slate, tile, or the like, in contrast to the bed. 4. The ridge or top of a horizontal member or structure like a joist, rafter, or roof.
5. A principal rafter.
6. The extrados or top surface of an arch, often buried in the surrounding masonry.
7. A low-grade veneer used for the back ply in plywood construction.
8. The wainscoting below the sash frame of a window, extending to the
floor.