What is the procedure called that may serve either a single airport or more than one airport upon arrival?

The procedure that serves either a single airport or multiple airports upon arrival is known as a Standard Terminal Arrival Route, or STAR. STARs are established routes designed to guide arriving aircraft from the en route phase of flight to the vicinity of an airport, allowing for a more standardized and predictable approach.

STARs are particularly useful because they help to manage air traffic in busy terminal areas by providing a structured way for aircraft to transition from higher altitude en route flight to the lower altitude approaches that lead directly to an airport. These procedures can incorporate waypoints and altitudes that facilitate a smooth integration of arriving aircraft, minimizing delays and enhancing safety in crowded airspace.

While the other options are relevant to aviation operations, they serve different purposes. Standard Instrument Departures (SIDs) are utilized for departures from airports rather than arrivals. Instrument Approach Procedures (IAPs) specifically provide the details necessary for approaching and landing at an airport. Controlled Airspace Routing is a broader term referring to the management of air traffic within controlled airspace, which does not specifically relate to the structured paths that arriving aircraft follow like STARs do.