Global Distribution System (GDS) is a database that stores and updates information on travel products worldwide. The four major GDS are Amadeus, Galileo, Sabre, and Worldspan. GDS enables travel agents to access and book flights, hotels, cars, and other travel services in real-time. GDS evolved from airline computer reservation systems and now operate independently while connecting travel suppliers and agencies globally. They provide availability, pricing, and booking capabilities for a wide range of travel products.