What does "authorization by ATC for a pilot to conduct an instrument approach" refer to?

The term "authorization by ATC for a pilot to conduct an instrument approach" specifically refers to approach clearance. This clearance is a vital part of the air traffic control process, as it indicates that ATC has approved the pilot to begin the specific instrument approach procedure that leads to landing at an airport. It ensures that the pilot can safely navigate the approach while maintaining separation from other aircraft and adhering to the established flight path and altitudes.

In contrast, holding clearance refers to instructions given to an aircraft to enter a holding pattern, typically to delay its approach or landing. Landing clearance is what a pilot receives once they are on the final approach to the runway, allowing them to land. Flight plan clearance pertains to the approval of the entire route for a flight but does not specifically address the process of approaching and landing at an airport. Thus, the most accurate term related to ATC authorization for conducting an instrument approach is indeed approach clearance.