Plain English Meaning
The exact speeds the manufacturer says you should fly at during each part of a flight. Flying at these speeds keeps the airplane safe and performing the way it was designed to.
Full Definition
The specific airspeeds published by the aircraft manufacturer for each phase of flight and flight condition, including takeoff, climb, cruise, approach, landing, maneuvering, and emergency operations. These airspeeds are listed in the Pilot's Operating Handbook (POH) or Airplane Flight Manual (AFM) and are intended to produce safe, efficient, and predictable when flown accurately.