An oblate spheroid is an ellipsoid produced by rotating an ellipse through 360° about its minor axis
(i.e., its shorter axis). An oblate spheroid is a sphere that is squashed
at its poles and swollen at its equator. The Earth, like most rotating,
roughly spherical objects in space, is an oblate spheroid, as Isaac Newton first proposed, the distance from Earth's center to sea level being roughly
13 miles (21 kilometers) greater at the equator than at the poles.
Compare with prolate spheroid.
See also oblateness.