Definition:Polar Coordinates/Radial Coordinate

Definition
Let $P$ be a point in a system of polar coordinates where $O$ is the pole.

The length of $OP$ is called the radial coordinate of $P$, and usually labelled $r$.

Also known as
The radial coordinate of $P$ can also be found referred to as the radius of $P$, but this terminology can be ambiguous.

Some sources give this as radius vector.

Also see

 * Definition:Angular Coordinate