An oblate spheroid is a rotationally symmetric ellipsoid having a polar axis shorter than the diameter of the equatorial circle whose plane bisects it. Oblate spheroids stand in contrast to prolate spheroids.
It can be formed by rotating an ellipse about its minor axis, forming an equator with the end points of the major axis. As with all ellipsoids, it can also be described by the lengths of three mutually perpendicular principal axes, which are in this case two arbitrary equatorial semi-major axes and one semi-minor axis.
An everyday example of an oblate spheroid is the shape of confectionery such as Smarties or M&M's. The shape of the Earth is very close to that of an oblate spheroid. Though local topography deviates from this idealized spheroid, on a global scale these deviations are very small.
Read more about Oblate Spheroid: Properties, Aspect Ratio