In which area do customs and border protection primarily operate at an airport?

Customs and Border Protection (CBP) primarily operates in the international arrivals area of an airport. This area is specifically designed for processing passengers returning from international flights. Upon disembarkation, travelers from international flights are required to go through customs and immigration checks to ensure that regulatory standards are met for entry into the country. CBP officers verify travel documents, check for contraband, and assess any applicable duties on items that travelers may be bringing into the country.

The terminal area for passenger check-in, while essential for the airport's overall operation, is primarily focused on ticketing, baggage check-in, and initial screening rather than customs procedures. The secured airside area is designated for operations involving aircraft and other security-related activities but does not involve customs and border activities. The baggage claim area, while important for retrieving luggage after a flight, is not the primary focus of CBP operations as this occurs after customs clearance is completed. The international arrivals area is the key point where customs checks take place, making it the correct answer.