The fictional world in C.S. Lewis's series is called Narnia.
Narnia is both the name of the wider fantasy world and the kingdom at the center of many of the stories. It contains talking animals, dwarfs, giants, witches, and other magical beings. The character Aslan, a great lion, is the world’s central guide and ruler.
The books also include neighboring regions such as Archenland, Calormen, and the country of Bism. Because readers often compare Lewis’s work with other fantasy traditions, Narnia is sometimes confused with Middle-earth from J.R.R. Tolkien’s writings or Prydain from Lloyd Alexander’s novels. Those are separate fictional settings created by different authors.