(pathology) a small abnormal patch on or inside the body
"The doctor noticed a painful plaque forming on the patient's gums during the routine examination."
a memorial made of brass
"The city installed a commemorative plaque of polished brass on the wall to honor the fallen soldiers."
Any flat, thin piece of clay, ivory, metal, etc., used for ornament, or for painting pictures upon, as a dish, plate, slab, etc., hung upon a wall; also, a smaller decoration worn by a person, such as a brooch.
"The museum displayed an ancient plaque of carved ivory that depicted scenes from mythology."
In plain English: A plaque is a hard, often crusty buildup that forms on surfaces and can be harmful if not cleaned off.
"The doctor removed the plaque from my teeth during cleaning."
Usage: In everyday usage, plaque refers to the hard deposit that builds up on teeth and gums rather than decorative flat pieces. You should use this word when describing dental hygiene issues instead of synonyms like tartar or calculus.
The word plaque comes directly from French, where it originally meant "plate," "sheet of metal," or a slab. It entered English with this same sense of a flat surface layer before later acquiring the medical meaning for bacteria on teeth.