Polar coordinate system
twodimensional coordinate system in which each point on a plane is determined by a distance from a reference point and an angle from a reference direction
In a polar coordinate system, a point is refered to by numbers including at least one distance r and one angle θ.

To represent the orientation of an object in space, three angles must be used. This can be viewed as a generalization of the spherical coordinates: ρ is not of interest, but an additional angle ω must be defined; however, this is not the standard way to define an orientation, one uses instead the Euler angles