Definition:Orbit (Physics)/Radius

Definition
Let body $A$ be in orbit around body $B$. Let $\mathbf r$ be the position vector of the center of mass of $A$ the center of mass of $B$ at a particular point in time.

The radius of the orbit of $A$ around $B$ is defined as:
 * the position vector $\mathbf r$

or
 * the length of $\mathbf r$.

Context will determine which is meant.