I have heard of the terms slice, segment and leg. Since I am a newbie in travel industry, I would like to know and understand the basic differences between the three.

Could someone please explain the three, using some kind of example?

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    $\begingroup$ Looks more from food industry $\endgroup$ – Trebia Project. May 5 '15 at 8:49
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    $\begingroup$ @TrebiaProject. or something from math.SE ;) $\endgroup$ – dalearn May 29 '18 at 0:26

I'm pretty sure those terms are not used consistently across all organisations in the air travel industry.

They are not defined in an IATA glossary I looked at but I did find this:

Definition of Flight Segment

The International Air Transport Association (IATA), the international trade body for airlines around the world, defines a flight segment as the operation of a flight with a single flight designator between the point where passengers first board an aircraft and the passengers' final destination. A flight designator includes an airline code, which has two letters or a number and a letter in combination, and a flight number of up to four digits. A flight segment can include any number of stops where passengers board and deplane the same aircraft operated by a single airline.

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.

From eHow

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  • $\begingroup$ Segment is used pretty consistently, simply because the major booking organisations (Sabre, Amadeus et al) use it in the same way. The "PNR, Passenger, Segment, Seat" relationship is universal, in my experience $\endgroup$ – Jon Story Oct 17 '16 at 15:04
  • $\begingroup$ This answer contradicts the quoted definitions from the IATA globssary below: There, a flight segment can theoretically involve an aircraft change at some airport as long as the flight number doesn't change. Can you please square this discrepancy? $\endgroup$ – einpoklum Jul 4 '19 at 12:06
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    $\begingroup$ @einpoklum A flight number may have two legs with diferent planes. For exampl, the segment BCN-MAD-SCL may be called IB-2312 where BCN-MAD is a leg and MAD-SCL is another. And both use diferent aircraft as the range is very different. $\endgroup$ – borjab Sep 21 at 21:28
  • $\begingroup$ @borjab: So, a flight is made up of one or more segments, which are made up of one or more legs each. Segments end when the aircraft is changed (or at the last endpoint). But - can there be de-planing/disembarkation between the legs of a single a segment? $\endgroup$ – einpoklum Sep 21 at 21:52

From IATA passenger glossary:


The operation between a departure station and the next arrival station.


  1. A leg or a group of legs from boarding point of a passenger to a deplaning point on a given flight.

  2. Sometimes referred to as "City Pair". The operation between board point and any subsequent off point within the same flight number.

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.

It is the first time I have heard the slice term.

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    $\begingroup$ The link is no longer working. $\endgroup$ – Preet Sangha Aug 17 '18 at 3:02
  • $\begingroup$ Updated. Thanks @PreetSangha $\endgroup$ – borjab Aug 17 '18 at 8:29
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    $\begingroup$ Update to the IATA page, the Airline Industry Data Model has a glossary in .xls format attached as a Resource iata.org/en/programs/passenger/industry-data-model $\endgroup$ – Alx Sep 21 at 19:00
  • $\begingroup$ @Alx I have updated the link. But IATA has a tendency to change it without warning $\endgroup$ – borjab Sep 21 at 21:25
  • $\begingroup$ appreciate the update, especially for those who end up looking for it as I did. Placing a glossary in an excel sheet also is not the most discoverable place.. $\endgroup$ – Alx Sep 22 at 2:11

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

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    $\begingroup$ Welcome to Aviation! If you will take the tour, that will help you get a good feel for the place. It looks like you've got a nice answer, it would be a great answer if you could tell us who the "Others" are that provide these definitions. Possibly include a link to where we could do more searching would be great too! $\endgroup$ – FreeMan Nov 1 '17 at 20:24

I am directly quoting from the book 'A Dictionary of Travel and Tourism Terminology' by Allan Beaver.

"sector, segment or leg: A sector is, by definition, a portion of an itinerary, or journey, which may consist of one or more legs or segments. A leg is the portion of a journey between two consecutive scheduled stops on any particular flight. A segment is that portion of a journey, from a boarding point of a passenger, to a deplaning point of the given flight. Although the passenger may not leave the plane, it may tough down to take on or let off passengers at several points, so that a segment may be made up of a leg or group of legs."

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