Final answer:
The term used in aviation to acknowledge the transfer of an aircraft between controllers is 'Radar Contact'. This indicates that the aircraft is identified and ready to enter the new airspace under the guidance of the receiving controller.
Step-by-step explanation:
In aviation, when coordinating the transfer of an aircraft from one air traffic controller to another, the term used to inform the controller initiating a handoff that the aircraft is identified and approval is granted for the aircraft to enter the receiving controller’s airspace is B) Radar Contact. This acknowledgement signifies that the receiving controller has the aircraft on radar and is ready to provide air traffic services. This process is crucial for maintaining the safe and efficient flow of air traffic.