A gradual accumulation of debris upon which a continuously occupied settlement is built, or which is the by-product or remains of some activity. The term can mean (1) a constructed earthwork or fortification, especially one with a geometric or animal form (also called effigy mound), (2) a low, isolated, rounded natural hill, usually of earth, (3) a structure built by fossil colonial organisms, (4) prehistoric refuse heap consisting chiefly of the shells of edible mollusks (also called shell mound), or (5) an artificial construction commonly used for human burial (also called burial mound) or as a foundation for a temple or dwelling.