They are partially correct.

It consists of a slightly convex disc (complete with edge-of-the-world drop-off and consequent waterfall) resting on the backs of four huge elephants which are in turn standing on the back of an enormous turtle, named Great A'Tuin, (similar to Chukwa or Akupara from Hindu mythology, though "world turtles" are common to many disparate cosmologies) as it slowly swims through space.

As thought by Sir Terry Pratchett.

http://discworld.wikia.com/wiki/Discworld