Most planets, like our own Roundworld, are spherical bodies that spin on their axis whilst caught in an interplanetary gravitational waltz around a central star. The Discworld has no such predictability or adherence to the laws of physics. The Disc is a flat earth, a circular plane supported by four gigantic elephants which stand on the carapace of Great A’Tuin, the world turtle.

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from: https://terrypratchett.com/explore-discworld/great-atuin-and-the-discworld/