boss

   A circular bulge or knoblike form, as a round mound protrudes from a flatter area surrounding it. Also, such a raised area used as ornamentation. In architecture, a raised ornament, such as one where the ribs in a vaulted roof intersect. The raised or protruding parts of work are sometimes referred to as bosses, hills, ridges, or mountains, etc., as opposed to the recessed portions in terms of valleys, canyons, hollows, or ditches, etc.