GDS: What are hotel booking engines?

If you have a hotel booking website, then you are familiar with this term. Booking engines are online booking systems such as the GDS (Global Distribution Solution), that are built from the information from several travel agencies.
These IBEs (Internet Booking Engines), help the travel and tourism industry for booking hotels, flights, holiday packages, and other services.
GDS for Hotels
The GDS is a large computer network that passes inventory and rates for hotels to travel agents and travel sites. It can be used by cars and airlines as well. The information of the GDS comes from info collected by travel agents systems such as Amadeus, Galileo, Sabre, Pegasus and Worldspan.
Properties should be defined in the GDS and will be available in the large database. Their information, such as their price, availability, rates, etc. should all be updated constantly in the GDS. Whether your a hotel or an airline, the booking engine should be up to date. Once the info is updated, it will display in search results of hotel booking websites, and travel agency websites.
You can see a list of GDS travel agent systems and prices here.
Here are some features of the GDS:

• it's 24/7 available and working
• it connects different systems seamlessly
• vast coverage for agents and travelers. 
• little maintenance effort required and automatically copies info from the hotel chain

Other references:
http://www.foretechnology.com/Blog/2015/January/what-is-GDS.html