a shape that is generated by rotating an ellipse around one of its axes; "it looked like a sphere but on closer examination I saw it was really a spheroid"
Mathematical figure closely approaching the geoid in form and size and used as a surface of reference for geodetic surveys A reference spheroid or ellipsoid is a spheroid determined by revolving an ellipse about its shorter (polar) axis and used as a base for geodetic surveys of a large section of the Earth (such as the Clarke spheroid of 1866 which is used for geodetic surveys in the United States)
an ellipsoid in which two of the three axes are equal (Contrast to an ellipsoid, in which all three axes may have different lengths ) A spheroid has the equation (x²+y²)/a² + z²/c² = 1