Oulu Airport carries the IATA code OUL — the three letters printed on boarding passes and baggage tags — and the ICAO code EFOU, used in flight plans and by air traffic control. It serves Oulu / Oulunsalo, Finland.
IATA codes are assigned by the International Air Transport Association for passenger-facing use; the four-letter ICAO code encodes region and country and belongs to the operational side of aviation.