The relative velocity of an object with respect to another object is the rate at which it changes its position relative to the object / point taken as reference. For example, if vA and vB are the velocities of the two objects along a straight line, the relative velocity of B with respect to A will be vB – vA.

The rate of change of the relative position of an object with respect to the other object is known as the relative velocity of that object with respect to the other.