City pair
A city pair in the commercial aviation industry means two codes on a flight itinerary that stand for departure and arrival airports. In other words, it’s a pair of airport codes between which scheduled air service is established. It can be direct or connecting flights by one or multiple air carriers.
Notably, codes in the city pair can either mean specific airports (e.g., in the city pair JFK-LHR, JFK stands for John F. Kennedy International Airport and LHR stands for London Heathrow) or metropolitan areas that have several airports (e.g., NYC-PAR, where NYC stands for any of the three airports that serve New York City and PAR stands for any of the four Paris airports).