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.
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