(1) One of a set of three coordinates in a spherical coordinate system. (2) A coordinate in a coordinate system on a sphere. Usually, two coordinates, in angular or linear units, fix the location of a point with respect to two great circles that intersect at right angles. However, the coordinates may be the great circle distances from two points on the sphere or may be the distance along one great circle and distance from another. The term is sometimes used to designate a coordinate on any surface approximately spherical.