The Polar Coordinate System describes points in space using a radius and angle relative to the origin. Angles are measured using radians, where a full rotation around the circle is equal to the circle constant (tau) where radians. By convention angles are measured from what is considered the positive direction in the cartesian coordinate system with the positive angle direction as counter-clockwise.
A point is denoted with two variables: which represents the radius corresponding to the point and which represents the angle corresponding to the point. The interactive below demonstrates some example points in the coordinate system.