Plain English Meaning
The speed the airplane must reach before you raise the gear or flaps. Below this speed, raising them too early can cause a loss of lift or a sink toward the ground.
Full Definition
The minimum airspeed at which the landing gear and/or flaps may be safely retracted after takeoff or during a go-around, as specified by the airplane manufacturer in the Pilot's Operating Handbook (POH) or Airplane Flight Manual (AFM).
Context Anchor
Seen during go-around procedures, especially when changing from a landing setup to a climb setup after deciding not to land.