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
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.