Middle-earth is the setting of much of J. R. R. Tolkien's legendarium. The term is equivalent to the term Midgard of Norse mythology, describing the human-inhabited world, i.e. the central continent of world of Tolkien's imagined mythological past. Tolkien's most widely read works, The Hobbit and The Lord of the Rings take place entirely in Middle-earth, and Middle-earth has also become a short-hand to refer to the legendarium or its "fictional-universe".
Within his stories, Tolkien translated the name "Middle-earth" as Endor (or sometimes Endórë) and Ennor in the Elvish languages Quenya and Sindarin respectively, sometimes referring only to the continent that the stories take place on, with another southern continent called the Dark Land.
Middle-earth is the central continent of Earth (Arda) in an imaginary period of the Earth's past (Tolkien placed the end of the Third Age at about 6,000 years before his own time), in the sense of a "secondary or sub-creational reality". Its general position is reminiscent of Europe, with the environs of the Shire intended to be reminiscent of England (more specifically, the West Midlands, with Hobbiton set at the same latitude as Oxford).
Far, where dawn never ends
Away, are echoes the old lady sings
Crying that years
Years I've been trapped in this cave
Inside, a candle consumed by its flame
And all of the repenting words aside
I desire to hurt you
Desert the world you belong to
In the forest where I lay
My hungry heart
My mellow mind
All my thoughts
They're weak in kind
They're dreams
Red is the mountain of mice
Rotten on the hour of demise
The pile, it resembles a crown
And every roaring squel
Is shame in disguise
Coming clear
And all that you wished for
Is becoming right now
Still it stays, in troubling ways
The ire
Far, where dawn never ends
Away, the old lady sings
For years I've been trapped in this cave