类球面是一种二次曲面。二维的椭圆有两个主轴，称为长轴与短轴。在三维空间里，将一个椭圆绕着其任何一主轴旋转，则可得到一个类球面。

用另外一种方法来描述，类球面是一种椭球面。采用直角坐标，椭球面可以表达为

其中，与分别是椭球面在x-轴与y-轴的赤道半径，是椭球面在z-轴的极半径．这三个正值实数的半径决定了椭球面的形状。

A spheroid, or ellipsoid of revolution, is 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 is rotated about its major axis, the result is a prolate (elongated) spheroid, like an American football or rugby ball. If the ellipse is rotated about its minor axis, the result is an oblate (flattened) spheroid, like a lentil. If the generating ellipse is a circle, the result is a sphere. A spheroid has circular symmetry.