What Are Flight Segments in Aviation?

The terms associated with air flights might sound very foreign if you are not a seasoned traveler. Flight segment is a term typically applied to portions of an itinerary where you will land in multiple cities along the way. However, technically all flights have at least one flight segment on a nonstop flight, the segment is from the city where you take off to your final destination.

Look for the term "stop" when choosing a flight itinerary. For example, if you see "2 Stops" next to a flight, you will land twice en route to your final destination. According to the International Air Transport Association, or IATA, flight segments refer only to stops where the next flight continues under the same flight number. Every stop adds another flight segment. For instance, if you have two stops under the same flight number, you will have three flight segments: city A to city B, city B to city C and city C to city D.

Pay attention to the amount of time between segments. If you are traveling from Los Angeles to New York with a stop in Chicago, for instance, compare the landing time for the Los Angeles to New York segment with the take-off time for the Chicago to New York segment. If the time between segments is very short, you are more likely to miss your second segment in the event the first flight runs behind. Choose a flight with at least one full hour between segments to give yourself some wiggle room.

Comparison of Flights and Legs

A flight is defined by the IATA as the operation of one or more flight legs with the same flight designator. Unlike a flight segment, a flight may involve one or more aircraft. The IATA defines a leg as the operation of an aircraft from one scheduled departure station to its next scheduled arrival station. A flight segment can include one or more legs operated by a single aircraft with the same flight designator.

Leg vs Segment in layman terms:

A leg stops when the plane lands. A segment stops either when you change flight number of when you arrive at one city where you want to spend time. One segment includes one or more legs from the same flight number. Sometimes a plane lands to refuel or to load other passengers but is technically the same flight number. Every ticket's coupon represent a segment.

As defined by others:

A leg is always a single non-stop flight. Example, UA123 from BOS-EWR is a leg.

A segment is a flight operated by a single flight number, but may have an intermediate stop....Example - UA 234 from BOS-ORD-SFO is a segment "Slice" is a newer and less used term in the travel industry:

A slice can be a single flight segment or multiple flight segments to get from origin to destination, possibly with a connection, but without a stopover.

Example- round trip itinerary with two slices

Slice 1 - UA123/15NOV BOS-EWR Slice 1 - UA234/15NOV EWR-SFO

Slice 2 - UA345/25NOV SFO-BOS