Ellipsoid (noun)

1. A solid figure that is a three-dimensional representation of an ellipse, the shape of which can be described mathematically by a set of points in space such that the sum of the distances from any point on the surface of the solid to two fixed points is constant.
2. A mathematical representation of an ellipse that is used to describe the earth's shape and gravity field.

Origin:

Late 16th century: from french ellipsoïde, from greek elleipsis "ellipsis" + -oïde "-oid".

Examples:

1. The earth is approximately an oblate spheroid, which means it is slightly flattened at the poles and bulging at the equator.
2. Scientists use mathematical models of the ellipsoid to make predictions about the earth's gravity field.
3. An ellipsoid is a geometric shape that can be described by three semi-axes and three orthogonal axes.
4. The surface of the ellipsoid can be parameterized in many different ways, depending on the application.
5. Ellipsoids are used in many areas of science and engineering, including geodesy, navigation, and control systems.