Flight coupon

A flight coupon is a document or electronic record that serves as evidence of a purchased air travel service. It corresponds to a specific segment of a trip.

Flight coupons also help ensure that passengers follow the intended travel itinerary. For example, a traveler books a round trip that looks like this: New York (JFK) → London (LHR) → New York (JFK). 

If a passenger skips a segment—from JFK to LHR, the airline will likely cancel the return flight automatically. This is because round-trip fares are often much cheaper than booking one-way tickets separately, and airlines use this rule to prevent fare abuse.