A piece of decorative trim installed along the top edge of a flat baseboard. It transitions the thick baseboard material smoothly into the wall drywall or plaster. Carpenters use it to build up complex, custom profiles from standard flat stock, hiding any gaps caused by wavy walls.
Heard on the job
Run a bead of caulk along the base cap before you paint the trim.
Insider tip
Using a separate base cap and flat board is often cheaper and easier to bend around curved walls than buying a single thick piece of milled molding.