Cylindrical coordinate system

A cylindrical coordinate system is a three-dimensional coordinate system that specifies point positions around a main axis (a chosen directed line) and an auxiliary axis (a reference ray). The three cylindrical coordinates are: the point perpendicular distance ρ from the main axis; the point signed distance z along the main axis from a chosen origin; and the plane angle φ of the point projection on a reference plane (passing through the origin and perpendicular to the main axis) The main axis is variously called the cylindrical or longitudinal axis.

Source: Wikipedia — Cylindrical coordinate system (CC BY-SA 4.0)