What type of clearance is needed for aircraft to taxi on the runway?

Taxi clearance is required for aircraft to move on the runway. This clearance informs pilots that they are authorized to move from their parking location to the runway or between runways and taxiways. It is a critical aspect of air traffic control operations, ensuring that the aircraft move safely and efficiently on the ground, avoiding any conflicts with other aircraft or vehicles operating in the vicinity.

Approach clearance is needed for an aircraft that is transitioning to land but does not apply to taxiing operations. Landing clearance is granted when an aircraft is about to touch down on a runway. Takeoff clearance is necessary before an aircraft can actually depart from the runway but does not pertain to taxiing movements. Thus, taxi clearance specifically governs the procedures for moving an aircraft on the ground, making it the correct choice in this context.