Middle-earth is a fictional fantasy world invented by J. R. R. Tolkien. Several of his books take place there, such as The Hobbit and The Lord of the Rings. It is supposed to be a long gone mythological time of our earth.
Although Middle-earth is only one continent in Tolkien's world, it is often used for the whole fictional world and all stories Tolkien invented for it. Tolkien created and worked on Middle-earth through most of his life, and it is this creation for which he is most famous.
Middle-earth has its own geography, several different species and peoples (elves, dwarves, humans, hobbits), their languages, and a history that spans thousands of years. The stories of Middle-earth are also a kind of 'artificial myth'.
"Middle-earth" is called Endor (or Endóre) and Ennor in the fictional Elvish languages Quenya and Sindarin.