The fictional world in C.S. Lewis’s Narnia books is called Narnia.
Narnia is the central setting of The Chronicles of Narnia, a seven-book fantasy series. It is inhabited by talking animals, dwarfs, giants, fauns, centaurs, and other legendary beings. Human children from Earth enter the world at different points in its long history.
The name can refer both to the wider world and, in some contexts, to the kingdom at its center. The stories also include neighboring lands such as Archenland and Calormen, along with places like the Eastern Ocean and the world of Aslan’s creation.
Narnia is often confused with Middle-earth, the setting created by J.R.R. Tolkien. The two worlds belong to different authors and fictional traditions, although Lewis and Tolkien were close friends and members of the Inklings.