- A patch or small differentiated area on a body surface (skin, mucosa, or arterial endothelium) or on the cut surface of an organ such as the brain; in skin, a circumscribed, elevated, superficial, and solid area exceeding 1 cm in diameter.
- An area of clearing in a flat confluent growth of bacteria or tissue cells, such as that caused by the lytic action of bacteriophage in an agar plate culture of bacteria, by the cytopathic effect of certain animal viruses in a sheet of cultured tissue cells, or by antibody (hemolysin) produced by lymphocytes cultured in the presence of erythrocytes and to which complement has been added.
- A sharply defined zone of demyelination characteristic of multiple sclerosis.
See: dental plaque
[Fr. a plate]