These are just IATA (International Air Transport Association) codes. They are used in aviation to identify and differentiate airports. That’s why a Iloilo City Mandurriao Airport to Frankfurt am Main Airport flight would often be abbreviated as a ILO to FRA flight. Berlin Brandenburg Airport (BER), Munich Franz Josef Strauss Airport (MUC), Duesseldorf Intl Airport (DUS), Hamburg Airport (HAM), Stuttgart Echterdingen Airport (STR) are other airports near this flight route and their unique identifiers/IATA codes. Find deals