The ellipsoid, also known as the egg shape or prolate spheroid, is a quadric surface that generalizes the sphere in two independent directions. It is defined as the image of a hyperbola rotated 90 degrees about its latus rectum.
In the world of geometry, the ellipsoid is often used to model the shape of, say, an alien spaceship or a particularly large, oblong melon.
For more information, see Rotation in Geometry.