international airport

An international airport is an airport typically equipped with customs and immigration facilities to handle international flights to and from other countries. Such airports are usually larger, and often feature longer runways and facilities to accommodate the large aircraft commonly used for international or intercontinental travel. International airports often host domestic flights (flights which take place inside only one country) in addition to international flights. In many smaller countries most airports are international airports, so the concept of an "international airport" has little meaning. In certain countries however, there is a sub-category of limited international airports which handle international flights, but are limited to short-haul destinations (often due to geographical factors) or are mixed civilian/military airports.
See more at Wikipedia.org...

1) Any airport designated by the Contracting State in whose territory it is situated as an airport of entry and departure for international air traffic. 2) An airport of entry which has been designated by the Secretary of Treasury or Commissioner of Customs as an international airport for customs service. 3) A landing rights airport at which specific permission to land must be obtained from customs authorities in advance of contemplated use. 4) Airports designated under the Convention on International Civil Aviation as an airport for use by international commercial air transport and/or international general aviation. (FAA4)

[ICAO]
Any airport designated by the Contracting State in whose territory it is situated as an airport of entry and departure for international air traffic, where the formalities incident to customs, immigration, public health, animal and plant quarantine and similar procedures are carried out.
 

Relating to international flight, it means:

a. An airport of entry which has been designated by the Secretary of Treasury or Commissioner of Customs as an international airport for customs service.

b. A landing rights airport at which specific permission to land must be obtained from customs authorities in advance of contemplated use.

c. Airports designated under the Convention on International Civil Aviation as an airport for use by international commercial air transport and/or international general aviation.
(See ICAO term INTERNATIONAL AIRPORT.)
(Refer to AIRPORT/FACILITY DIRECTORY.)
(Refer to IFIM.)