Air Travel Terminology

*Be Aware… Air Travel Industry terminology can be quite confusing.  Terms are often misused, but can also have legitimately different meanings in various contexts.  Terms which require context to determine the exact meaning are noted with an asterisk (*).  Some organizations and businesses may use slightly different definitions for some of the terms in this document, but the definitions shown here are the most widely accepted throughout the industry.




An Alliance is a group of airlines (known as Member Airlines) which have agreed to work together and share resources to some extent.  The Member Airlines of an Alliance may be thought of as Partner Airlines in a partnership of more than two airlines.  Shared resources may include Codesharing, assisting each other’s passengers with travel arrangements, accommodating each other’s passengers due to schedule disruption, allowing customers to share Frequent Flyer privileges and benefits among member airlines, allowing customers to use the facilities (such as clubs and lounges) of member airlines, and others.  Frequent Flyers do not necessarily have all of their frequent Flyer privileges with all member airlines in the alliance.  Popular alliances are oneworld, SkyTeam, and Star Alliance.


Carrier (or Air Carrier) is an industry term that is synonymous with Airline.  Get used to seeing it because the airlines use Carrier to refer to themselves in most cases.


Flag refers to the country in which an airline is registered.  For example, Delta Airlines is a U.S. Flag Carrier.

Flight Number

A unique composite identifier for a Direct or Nonstop flight, consisting of an alphanumeric airline identifier and a numerical flight number identifier.  The airline prefix usually seen by the customer is the IATA 2-character airline identifier, although pilots and air traffic controllers usually use the ICAO 3-letter airline identifier.  Example:  DL1234 or DAL1234 indicates Delta Airlines Flight 1234.  The airline identifier may be omitted when it is clear which airline is being discussed (i.e. “Flight 1234”).  Occasionally, a flight number identifier may include alphabetic characters, for operational requirements (i.e. “DL234A”).

Frequent Flyer

As used in this document, a Frequent Flyer is a member of an airline’s customer loyalty program, and not just a colloquial term for someone who travels frequently.  Frequent Flyer specifically refers to an official and registered member of an airline-operated program, not just a credit card mileage or other affiliate program.  For example, to be a Frequent Flyer with Delta Airlines, you must actually be an enrolled member of Delta’s SkyMiles program.


International Air Transport Association.  The primary trade association for the world’s airlines.  IATA seeks to promote the airline industry and has members in the airline and travel industries all over the world.  IATA issues the 3-letter airport and 2-character airline codes with which passengers are most familiar.


International Civil Aviation Organization.  A specialized agency of the United Nations which seeks to promote cooperation and uniformity in civil (non-military) aviation throughout the world.  ICAO issues the 4-character airport and 3-character airline codes with which pilots and air traffic controllers are most familiar.


The (usually painted) insignia, logo, and distinctive markings on the outside of an aircraft, which usually (but not always) indicates the identity of the Operating Carrier.

Examples of Livery on Boeing 777:  in Delta Livery (first image) and in SkyTeam livery (second image, Air France)

Member Airline

When an airline is part of an Alliance, it is said to be a Member Airline of that Alliance.

Operating Carrier

The Operating Carrier is the airline which is actually operating a flight, regardless of the airline (flight) name on the Ticket or the Livery on the aircraft.  Operating Carrier is often used in reference to Codeshares.

Partner Airline

Partner Airlines are airlines which have agreed to work together and share resources to some extent.  Shared resources may include Codesharing, assisting each other’s passengers with travel arrangements, accommodating each other’s passengers due to schedule disruption, allowing customers to share each other’s Frequent Flyer privileges and benefits, allowing customers to use each other’s facilities (such as clubs and lounges), and others.  Frequent Flyers do not necessarily have all of their Frequent Flyer privileges and benefits with a Partner Airline.  A formal partnership involving more than two airlines may be organized as an Alliance.



A Codeshare is a flight operated by one Carrier but sold by another Carrier under its own brand.  Usually, the Carrier actually operating the flight is listed as the Operating Carrier on the Ticket, Itinerary, or Boarding Pass.  For example, Alpha Airlines might sell a seat on a Bravo Airlines flight, listed on the ticket as “Alpha 123, operated by Bravo Airlines.”  The numerical portions of the flight numbers are not necessarily the same.  For example, in the previous example, the flight known as Alpha 123 might be operated as Bravo 4856.  Seats sold as Codeshares are usually sold under an agreement with a Partner Airline or a Member Airline belonging to the same Alliance.

Contract of Carriage

The rules that constitute the agreement the customer makes with the airline when he purchases a ticket.  It outlines the responsibilities and rights of both the airline and the passenger.  The Contract of Carriage usually applies to all tickets issued by the airline, whereas Fare Rules are specific to the individual ticket.

Fare Basis

The Fare Basis (sometimes called Fare Code or Fare Basis Code) is a string of characters (usually 6 or more alphanumeric characters), usually (but not always) beginning with the letter indicating the Fare Class, which indicates the Fare Rules for the ticket.  Fare Basis characters are proprietary, and they vary among airlines (although there is some standardization within the industry).  Fare Basis Codes are not easily interpreted by the average customer/passenger.  However, the actual Fare Rules are usually written in plain language on a paper Ticket and can also be found on your airline’s website.  The Fare Basis may be different for some or all Segments on the same Ticketsee Fare Rules

Sample from United’s website:  On the first page, Fare Class is indicated; Click on View Fare Rules and the Fare Rules page, including the Fare Basis Code, is shown on the second page; Plain-text Fare Rules are shown below the Fare Basis Code on that web page (but not shown here) 

Fare Bucket

Fare Bucket refers to the “pool” of Fare Classes which are available for sale.  It is used colloquially to refer to the number of tickets available for a particular Fare Class.  For example, “Only 2 tickets are left in the ‘L’ Bucket.”

Fare Class

Usually referred to by a single letter (ex. “Y” for full-fare economy), the Fare Class or Booking Code of a Ticket indicates the Ticket’s Class of Service as well as the Ticket’s place in an airline’s Fare hierarchy.  Fare Classes vary among airlines, although many airlines do use the same codes for some tickets.  The Fare Class may be different for some or all Segments on the same Ticketsee Fare Bucket

Fare Rules

The rules that apply to a particular Ticket, as denoted by its Fare Basis.  This includes items such as minimum stay, upgradability, etc.

Online Travel Agency (OTA)

An entity that sells airline tickets and other travel arrangements, primarily via a website. Examples are Expedia and Orbitz.


An Op-Up (Operational Upgrade) is an involuntary re-assignment (upgrade), at no additional cost, of a passenger to a higher cabin class (class of service) than that included in the ticket.   Op-Ups are usually done at the gate, less than one hour prior to departure, and are usually done because the airline has oversold the cabin which the customer booked.  Op-Ups usually occur on long-haul flights with premium cabins, on which free upgrades are not normally offered, and are usually given to passengers who hold the highest Frequent Flyer Status with the airline, or passengers who have Tickets with the highest Fare Class in the next lower Class of Service.

Plating Carrier

The Plating Carrier is the airline which actually sells the Ticket, regardless of the airline(s) actually operating the Flight(s) on the Ticket (Operating Carrier).  The Plating Carrier usually (but not always) operates at least one flight on a Ticket that it sells.

The term “Plating” comes from the old-style ticket imprinters, similar to the old credit card imprinting machines that used to be common in retail stores.  Rather than a credit card, the airlines imprinted their tickets with a “Plate” containing the logo of the airline selling the ticket and other information.  Shown at left is an old Air France plate used to imprint tickets.


A Passenger Name Record (PNR) is a record in the database of a reservation system which contains a passenger’s entire Trip.  A PNR may include one or more passengers on the same Trip that are booked together (i.e. a family and/or friends traveling on a Trip together).


A document (which may be electronic) that serves as a receipt and contract between a passenger and an airline for an entire Trip.  A Ticket is an agreement by the airline to transport the passenger in accordance with the Fare Rules and applicable laws.


Circle Trip

A Circle Trip is a Multi-stop Trip that uses the same airport as the Origin and Final Destination.


A Connection is a stop between Legs for the purpose of changing aircraft.  see Layover


Co-terminals are two or more airports serving the same area – typically a large city or metropolitan area.  Airlines usually, but not always, treat Co-terminals as the same airport for the purpose of ticket booking rules and fare computation (note: this does not mean that the fares to/from those airports will always be the same).  IATA usually assigns an identifier to the area that includes all airports that already have their own IATA identifiers, which is called a metropolitan area identifier.  For example, NYC is IATA’s metropolitan area identifier for the New York City metropolitan area, and includes the JFK, EWR, LGA, and SWF airports.  On most Airline and Online Travel Agency (OTA) websites, you can search for flights using the metropolitan area identifier to see search results for all of the airports in that area.


The last airport of arrival in an Itinerary.  Destination be used to refer to the destination airport on either half of a Round Trip Itinerary or a Stopover Airport.  When referring to the Destination at the very end of a Trip the term Final Destination is often used.


A Direct Flight is a flight with one or more planned stops at a Connection Airport(s), but which retains the same flight number throughout the flight.  The reason for the stop may be to pick up/drop off passengers and/or cargo, to refuel, to clear immigration and customs controls, or other reasons.  A change of aircraft (Connection) may be required.  see Segment

Final Destination

The last airport of arrival at the very end of a Trip.


A Flight is any operation which retains the same Flight Number throughout.  Both Nonstops and Directs are Flights.  Make sure that you know exactly what is being discussed when the term Flight is used.  Some organizations and businesses use the term Flight as a generic term to refer to any aircraft operation.  The definition given here is the definition accepted by both ICAO and IATA.

Intermediate Stop

An Intermediate Stop is any stop other than the Final Destination of a Trip or the Destination of the first half of a Round Trip.  An Intermediate Stop may be a Layover, Connection, or Stopover.


Itinerary is an all-encompassing term that can have different meanings depending on the context.  The basic meaning of Itinerary is the entire sequence of Flights in a Trip.  However, Itinerary may also refer to a portion of a Trip, such as the sequence of flights between Origin and/or Stopover Airport on a Multi-stop Itinerary (i.e. “Denver to New York Itinerary”), or the Outbound and Return of a Round Trip Itinerary (i.e. “Outbound Itinerary”).  see Trip


Layover is a somewhat unofficial term that is used to refer to an Intermediate Stop that lasts significantly longer than is normally needed for a Connection or other Intermediate Stop, but is not a Stopover.  A Layover typically involves spending several hours at the airport or even spending the night at the airport or a nearby hotel.  A change of aircraft may or may not be required.


A Leg is an operation from one airport to another with no intermediate stops.  The Leg is the smallest component of any Trip.  All Flights consist of one or more Legs.  A Nonstop is not usually referred to as a Leg.


A Multi-stop is a Trip with at least one Stopover.


A Nonstop is a Flight from Origin to Destination with no intermediate stops.

One Way

A One Way is a Trip from Origin to Destination that has no Stopovers and does not return to the Origin.  A Trip that does not return to the Origin but has one or more Stopovers is referred to as a Multi-stop rather than a One Way.  Some travelers combine two or more One Ways to simulate a Round Trip or Multi-stop, usually because of a lower total price and/or additional flexibility.


An Open-ended Trip is a Trip with an undetermined departure date at a Stopover Airport.  When the Return half of a Round Trip has an undetermined departure date, it is usually called an Open Return.  This allows the passenger the flexibility of choosing the date of return or onward travel after the initial departure.  Open-ended tickets are not commonly seen at the present time.

Open Jaw

Open Jaw refers to a Stopover in a Trip which involves an arrival at one airport and a departure from another airport, requiring the passenger to arrange for other transportation between the two airports.  An Open Jaw is similar to any other Stopover in that the airline expects the passenger to depart the airport environment.  However, a passenger may simply use another Trip to close the Open Jaw for reasons of price and/or flexibility.


The first airport of departure on a TripOrigin may also refer to the point of departure after a Stopover or the departure airport at the beginning of the Return half of a Round Trip.


The first half of a Round Trip Itinerary, from Origin to Destination.


The second half of a Round Trip Itinerary, from the Destination of the Outbound half back to the Origin.  Return is also sometimes used synonymously with Round Trip (i.e. Return Ticket).

Round Trip

A Trip which proceeds from Origin to Destination, then returns to the Origin, with no Stopovers.  A Round Trip consists of an Outbound half and a Return half.  A Round Trip may include Intermediate Stops in either direction.  If there is a Stopover on either half of the Trip, the ticket is usually considered a Circle Trip rather than a Round Trip.


Around the World Trip (‘Round The World).  A Multi-stop Trip which circles the Earth.  To qualify, generally speaking, the Itinerary must go all the way (or most of the way) around the Earth in the same direction (either East or West) and contain at least five (5) stopovers.  However, airline rules and definitions of RTW do vary depending upon the airline(s) involved.  Airlines typically offer RTW tickets at reduced cost or reduced mileage redemption levels, compared to a typical Multi-stop.


A Segment is a Leg or a Direct Flight that does not require a change of aircraft.  Segment is usually only used to refer to a Segment that is part of a larger trip, rather than a Trip consisting of a single Leg or Direct Flight.  For Frequent Flyer qualification purposes, a Direct Flight may only count as one Segment, even if a change of aircraft is required.  Check with your airline to be sure.


A Stopover is an Intermediate Stop on a Multi-stop Trip where the airline acknowledges that the passenger will be spending time away from the airport visiting the area, as opposed to a Connection where the passenger is simply changing aircraft.  A Stopover lasts for at least 4 hours and is usually much longer, typically lasting for several days or even more than one week.  The location of the Stopover may be referred to as a Destination of an Itinerary or as a Stopover Airport.  The destination of the Outbound half of a Round Trip is usually not referred to as a Stopover, although it does meet the definition.


Transfer is synonymous with Connection.


A Trip is the entire sequence of Flights from Origin to Final Destination on a Ticketsee Itinerary

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