Cornice

A cornice is a projecting, usually molded band capping the top of a piece of case furniture (a bookcase, a highboy) or running around the top of a room where wall meets ceiling. On furniture, it's largely a decorative flourish -- visually finishing off the top of a tall piece with more presence than a bare flat top would have -- built up from one or more molding profiles mitered around the corners.

Because a cornice typically overhangs the case below it, it's usually built and attached as its own separate assembly rather than milled directly into the case top, both for ease of construction and so it can be sized generously without adding unnecessary bulk to the main carcase.