Rotational relative wind is the relative wind produced by the rotation of the rotor blades.
Rotational relative wind is parallel to the physical flight path of the rotor blades. The rotational relative wind is at its maximum velocity at the rotor tips.
FAA-H-8083-21A – Helicopter Flying Handbook pg. 2-8
Principles of Helicopter Flight, 2nd Edition, pg. 47
FM 3-04.203-2007 Fundamentals of Flight pg. 1-9