Which of the following is one of the four major global distribution systems?

Amadeus is one of the major global distribution systems (GDS) used widely in the travel industry to facilitate bookings, reservations, and travel-related transactions. A GDS is a network operated by a company that enables travel agencies and travel service providers to access and manage travel inventory, such as airline tickets, hotel rooms, and rental cars.

Worldspan is indeed one of the four key GDSs, along with Sabre, Amadeus, and Galileo. These systems serve as crucial tools for travel agents, providing them with access to large inventories and essential information necessary for planning and executing travel arrangements for clients.

In contrast, Expedia and Travelocity are online travel agencies (OTAs), which aggregate travel inventory for consumers but do not function as GDSs. They primarily facilitate travel bookings directly to the public, rather than serving as platforms for travel agencies to access travel content. Thus, while they are important in the travel ecosystem, they do not fall under the category of GDSs like Worldspan does.