Plain English Meaning
The speed you are flying at the moment you start the maneuver. You set this speed first, then begin.
Full Definition
The airspeed at which a pilot begins a specific flight maneuver. For a chandelle, it is the airspeed established before the maneuver starts, and must not exceed the airplane's maneuvering speed (V_A).
Context Anchor
Seen in maneuver instructions, such as setting up the airplane before starting a chandelle.
Why Pilots Care
Beginning at the correct entry airspeed gives the pilot the right amount of kinetic energy to trade for altitude through the 180-degree without or exceeding limits.