A nonstop flight
takes off from one runway and does not land until it reaches its
final destination. A direct flight refers to a flight that does not require a
plane change, but does stop along the way to its
destination, sometimes more than once.
Reservation
systems use a hierarchy. Nonstop flights get top priority,
followed by direct flights, followed by “through” flights
(which use one flight number, but involve a change of
planes), followed by connecting flights.