Airline hubs are airports ranked as large, medium, small, and non-hubs as one of the FAA airport categories which are re-evaluated every year based on number of commercial passengers.
The more common but informal use for the phrase 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 travelers moving between airports not served by direct flights change planes en route to their destinations.[citation needed] This is as opposed to the Point to Point model. Many hubs of the airlines are also situated at airports in the cities of the respective head offices.[citation needed]
Some airlines may use only a single hub, while other airlines use multiple hubs. Hubs are used for both passenger flights as well as cargo flights.[citation needed]
Many airlines also use focus cities, which function much the same as hubs. Airlines may also use secondary hubs, a non-technical term for large focus cities.[citation needed]
A hub in the middle of a route is more effective than at either end as connecting traffic more easily fills the plane - passengers prefer a one-stop (two-leg) route over a two-stop (three-leg) route.[1]