n ellipsoid is a type of quadric surface that is a higher dimensional analogue of an ellipse. The equation of a standard ellipsoid body in an x-y-z Cartesian coordinate system is
{x^2 \over a^2}+{y^2 \over b^2}+{z^2 \over c^2}=1
where a and b are the equatorial radii (along the x and y axes) and c is the polar radius (along the z-axis), all of which are fixed positive real numbers determining the shape of the ellipsoid.
If all three radii are equal, the solid body is a sphere; if two radii are equal, the ellipsoid is a spheroid:
* a=b=c:\,\! Sphere;
* a=b>c:\,\! Oblate spheroid (disk-shaped);
* a=b<c:\,\! Prolate spheroid (cigar-shaped);
* a>b>c:\,\! Scalene ellipsoid ("three unequal sides").
The points (a,0,0), (0,b,0) and (0,0,c) lie on the surface and the line segments from the origin to these points are called the semi-principal axes. These correspond to the semi-major axis and semi-minor axis of the appropriate ellipses.
http://en.wikipedia.org/wiki/Ellipsoid
^Wow, you're ignorant..