Currently, I'm studying how hotels manage bookings and promote them online. I just learned that hotels (or travel websites like Expedia) use Global Distribution Systems, GDS; examples are Worldspan, Pegasus, Amadeus, Galileo, Sabre & Abacus. But the question is 'What's GDS???' Can someone kindly explain to me as if I were a 10 years old?

Hi there,
A gds (global distribution system) is basically a computer reservation system that links travel agents (online and offline) to the airline system. In other words, if an agency wants to book a ticket on british airways, it will be very expensive for them to directly access the airline host system (databse) hence came the creation of the gds system (which initally wee all owned by airlines). There are 4 and now 3 GDS (sabre, amadeus and travelport combining worldspan and galileo). The gds contracts with the airlines to publish their content on the system, they also act like a tecnology provider for the airlines (host their system etc) then they sell the interface to the travel agents to enable them to make bookings. You can book airlines, hotels, car, etc within the GDS but it is very well know for the airline content primarly.
hope that helps.
R.