Induced flow is the downward vertical movement of air through the rotor system due to the production of lift, often referred to as downwash.At a hover in calm, no-wind conditions, the induced flow is at its greatest because there is no horizontal air flow affecting the rotor disc. Induced flow increases as the angle of attack of the rotor blades increases.
FAA-H-8083-21A – Helicopter Flying Handbook pg. 2-10
Principles of Helicopter Flight, 2nd Edition, pg. 47
FM 3-04.203-2007 Fundamentals of Flight pg. 1-9