oblate spheroid prolate spheroid A spheroid's a quadric surface obtained by rotating an ellipse about one of its principal axes; in other words, an ellipsoid with two equal semi-diameters. If the ellipse's rotated about its major axis, the result's a prolate (elongated) spheroid, like a rugby ball. If the ellipse's rotated about its minor axis, the result's an oblate (flattened) spheroid, like a lentil. If the generating ellipse's a circle, the result's a sphere. Because of its rotation,… (More on Spheroid)