A spheroid or ellipsoid of revolution is an ellipsoid such that two of the axes are equal in length. The name ellipsoid of revolution refers to the fact that such a shape is rotationally symmetric about the third axis. By way of contrast, the term triaxial ellipsoid is used to specify that the three axes are of different lengths. Also, the term oblate is used to describe spheriods in which the two axes of equal length are longer than the third (think of a doorknob) whilst the term prolate is used to describe spheriods for which the two equally long axes are shorter than the third axis (think of a cigar).