It constitutes most of his output and the every one is a satiric social commentary which just happens to be set on a 10,000 mile wide disc-shaped planet supported by four enormous elephants which are in turn standing on an even bigger tortoise. Oh, and it has wizards, gnomes, trolls, dwarves, witches, fairies, dragons, golems, vampires, werewolves and even some humans.
And the Pratchett quotes have been coming from me.....