Glossary

Travel involves a wide range of systems, institutions, and technical terminology that can be unfamiliar to many travelers. Airlines, immigration authorities, booking platforms, and transportation networks all use specialized language to describe how global travel operates.

This glossary explains common terms used in aviation, travel infrastructure, mobility systems, and international travel policies. Understanding these concepts helps travelers better interpret airline policies, visa rules, transportation systems, and travel data.

Some glossary entries link to related topic pages such as:

Over time, this glossary will expand as additional research and datasets are published.

Codeshare

A codeshare is an agreement between airlines that allows one airline to sell seats on a flight operated by another airline.

For example, a flight may be operated by one airline but marketed under multiple airline flight numbers. This allows airlines to expand their route networks without operating every flight themselves.

Codeshare agreements are common within airline alliances and are a key part of modern aviation networks.

Learn more about airline systems on the Aviation page:

Fifth Freedom Flight

A fifth freedom flight refers to a commercial aviation right that allows an airline to carry passengers between two foreign countries as part of a flight that begins or ends in its home country.

For example, an airline from Country A may operate a route from Country A to Country B and continue onward to Country C while carrying passengers between Country B and Country C.

These flights are regulated through international air service agreements and are relatively uncommon but important for global aviation connectivity.

Related topic:

Schengen Area

The Schengen Area is a group of European countries that have abolished internal border controls between participating states.

Travelers can move between Schengen countries without undergoing routine passport checks at internal borders. However, entry into the Schengen Area from outside the region is controlled through external border checks.

The Schengen Area operates under a shared visa system known as the Schengen Visa, which allows short-term travel across participating countries.

Related topic:

Transit Visa

A transit visa is a visa that allows travelers to pass through a country while traveling to another destination.

Transit visas are often required when a traveler must enter a country's territory temporarily while connecting between flights or changing airports. Requirements vary widely depending on nationality, airport procedures, and immigration policies.

Some countries require transit visas even if travelers remain within the airport's international transit area.

Related topic:

Global Distribution Systems (GDS)

A Global Distribution System (GDS) is a computerized network used by travel agencies, airlines, and booking platforms to access flight schedules, seat availability, and pricing information.

Major GDS platforms connect airlines, hotels, and travel service providers with travel agencies and online booking tools.

Examples of widely used GDS platforms include:

Amadeus
Sabre
Travelport

These systems form a core part of the digital infrastructure behind modern travel booking.

Related topic:

Airline Alliance

An airline alliance is a partnership between multiple airlines that cooperate on routes, scheduling, frequent flyer programs, and customer services.

Major global alliances include:

Star Alliance
Oneworld
SkyTeam

These alliances allow airlines to expand global connectivity while sharing operational benefits and coordinated scheduling.

Related topic:

Open-Jaw Flight

An open-jaw flight occurs when a traveler flies into one city but departs from another.

For example:

Arrival: Paris
Departure: Rome

Travelers arrange their own transportation between the two cities. Open-jaw tickets are common for multi-city itineraries and longer trips.

Bilateral Air Service Agreement

A bilateral air service agreement is a treaty between two countries that governs commercial aviation between them.

These agreements determine:

which airlines can operate routes
how many flights are allowed
which airports may be served
traffic rights such as fifth freedom flights

These agreements form the regulatory framework behind international aviation networks.

Related topic:

Interline Agreement

An interline agreement allows airlines to coordinate passenger travel across multiple carriers using a single ticket.

This means passengers can check luggage once and transfer between partner airlines during a journey.

Interline agreements help enable global airline connectivity even between airlines that are not part of the same alliance.

Related topic:

Jet Lag

Jet lag is a temporary sleep disorder caused by rapid travel across multiple time zones. The body’s internal circadian rhythm becomes misaligned with the local time at the destination.

Symptoms may include:

fatigue
sleep disruption
difficulty concentrating
digestive discomfort

Jet lag is most common on long-haul flights crossing several time zones.

Related topic:

Updating the Glossary

This glossary will expand over time as new topics, datasets, and research are published on Brandon Travel.

Suggestions and corrections are welcome.

See the Contribute page for more information: