Definition of: spherical coordinate system

Math.
A three–dimensional system for indicating the shape of a solid by means of a sphere with the pole at the center. A point is located in terms of its distance along its radius vector from the pole, and in terms of two angles
— the colatitude, or angle the radius vector forms with the vertical or polar axis of the sphere; and the longitude, or angle the radius vector makes with a fixed, vertical plane or initial meridian axis.