Oblate Spheroid

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

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Figure Of The Earth - Ellipsoid of Revolution
... used in geodesy to most nearly approximate Earth's shape is an oblate spheroid ... An oblate spheroid, or oblate ellipsoid, is an ellipsoid of revolution obtained by rotating an ellipse about its shorter axis ... A spheroid describing the figure of the Earth or other celestial body is called a reference ellipsoid ...
Oblate Spheroid - Aspect Ratio
... The aspect ratio of an oblate spheroid/ellipse, ba, is the ratio of the polar to equatorial lengths, while the flattening (also called oblateness) f ... The oblate spheroid is the approximate shape of many planets and celestial bodies, including Saturn and Altair, and – to a lesser extent – the Earth (with a = 6378.137 km and b ≈ 6356.752 km, providing an ...