Great question - ORD to MKY just means Chicago O'Hare Intl Airport to Mackay Airport. Now you’ll know what these unique codes when you look for flights! This flight route has multiple associated airports, so we think it might be helpful to learn the name and codes of them as well. They are Chicago Midway Airport (MDW), Moline Quad-City Airport (MLI), Greater Peoria Airport (PIA), Bloomington-Normal Airport (BMI), Champaign University-Willard Airport (CMI).