Spheroid
in geometry, a solid, resembling a sphere in form, and generated by the revolution of an ellipse about one of its axes. If an ellipse be revolved about its transverse axis, the spheroid generated is called a prolate spheroid; if it be revolved about its conjugate axis, the spheroid generated is called an oblate spheroid. The earth is an oblate spheroid that is, flattened at the poles so that its polar is less than its equatorial diameter.