ORD and CCU are unique codes to identify airports used in the aviation industry. They are defined by IATA (International Air Transport Association) and are commonly called IATA codes. ORD to CCU refers to a flight route from Chicago O'Hare Intl Airport to Kolkata Netaji S. Chandra Airport. Chicago Midway Airport (MDW), Chicago Greater Rockford Airport (RFD) are other airports near this flight route and their unique identifiers/IATA codes.