n. Any flat, thin piece of metal, clay, ivory, or the like, used for ornament, or for painting pictures upon, as a slab, plate, dish, or the like, hung upon a wall; also, a smaller decoration worn on the person, as a brooch.n. An accumulation of biofilm, or bacteria on teeth.n. Atheroma, an accumulation in artery walls made up of macrophage cells and debris containing lipids, (cholesterol and fatty acids), calcium, and connective tissue.n. A clearing in a bacterial lawn caused by a virus.