1. A reef, such as a coral reef, formed from organic material.
2. A mound-like accumulation of fossil remains on the site where organisms lived.
3. A mound, dome, or reef-like mass of rock that is composed almost exclusively of the remains of sedentary marine organisms; such as, corals, algae, mollusks, and other sedentary marine life; and is embedded in rock of a different physical character or lithology.