What is the difference between a layover and a stopover?

A layover is a connection where you change planes and continue, generally under 4 hours domestically and under 24 hours internationally depending on the carrier's definition. A stopover exceeds that threshold and is treated as an intentional visit rather than a transit. The distinction affects pricing, since a stopover may be ticketed differently, and it affects whether you need to collect bags, clear customs, or arrange accommodation. Several airlines actively market free or low-cost stopover programs, where a connection through their hub can be extended for days at no additional airfare, which is one of the few genuinely good deals left in air travel.

Practical points that cause the most trouble. Minimum connection time is set by the airport and airline, and booking below it is usually blocked, but a legal connection is not necessarily a comfortable one at a large international hub requiring a terminal change and a security rescreen. International connections in the United States require clearing immigration and customs and rechecking bags even when you are only transiting, which surprises travelers routing through American airports and eats far more time than expected. Separate tickets are the real risk: if a delay on the first causes you to miss the second, no airline owes you anything, whereas a single itinerary obligates the carrier to rebook you. And some countries require a transit visa even without leaving the airport, which is worth checking before assuming a connection is invisible.