any marine bivalve mollusk of the genus ostrea. they are usually found adhering to rocks or other fixed objects in shallow water along the seacoasts, or in brackish water in the mouth of rivers. the common european oyster (ostrea edulis), and the american oyster (ostrea virginiana), are the most important species.-a name popularly given to the delicate morsel contained in a small cavity of the bone on each side of the lower part of the back of a fowl.