Actually spelled Tlön. An imaginary world in a short story by Jorge Luis Borges called Tlön, Uqbar, Orbis Tertius. After an artifact from the world is discovered, researchers begin to create the Encyclopedia of Tlön, a description of the world (which has some interesting properties in itself). As the Encyclopedia near completion, Tlön increasingly impinges on the "real" world, until, by the end of the book, the original world has been almost eliminated and replaced by the world of Tlön.

Like other short stories, translated into English in the collection Labyrinths.