Final answer:
It is true that the phrase 'Radar Service Terminated' is used when ATC or a pilot decides to stop radar services for an aircraft, indicating a change in navigation responsibilities.
Step-by-step explanation:
True, whenever the controller or the pilot of an aircraft chooses to discontinue radar service, the phrase “Radar Service Terminated” is typically used. This phrase indicates that ATC will no longer provide radar services, such as traffic advisories and flight following. This can happen for several reasons, including when an aircraft leaves controlled airspace, when it's necessary for the pilot to resume navigation on their own, or when ATC's workload or radar coverage does not permit continued service.