An Airline Hub is an airport that an airline uses as a transfer point to get passengers to their intended destination. It is part of a hub-and-spoke model, where travellers moving between airports not served by direct flights change planes en route to their destinations. Many airline hubs are also located at airports in the cities of their respective head offices. Some airlines may use only a single hub, while other airlines use multiple hubs. Hubs are used for both passenger flights and cargo flights.