# Spheroid

A

**spheroid** is a

quadric surface in three dimensions obtained by rotating an

ellipse about one of its principal axes.
If the ellipse is rotated about its major axis, the surface is called a

*prolate spheroid* (similar to the shape of a

rugby ball).
If the minor axis is chosen, the surface is called an

*oblate spheroid* (similar to the shape of planet

Earth).

The sphere is a special case of the spheroid in which the generating ellipse is a circle.

A spheroid is a special case of an ellipsoid where two of the three major axes are equal.