A specialization of both round thing, two dimensional shape, and closed surface region (qq.v.). Each instance of ellipsoid is a two-dimensional unbounded surface, embedded in a three-dimensional space, and such that the planar sections along its respective internal axes are Ellipses (q.v.).

Note that sphere and its generalization spheroid are specializations of ellipsoid. See also ellipsoid, each instance of which is an (intangible or tangible) three-dimensional object whose boundary is or approximates an ellipsoid.