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).
Things are looking bad now
They never have been worse
To the north lie mountains
To the south a curse
Bloodstained footprints in the shifting sands
Among the olive groves of Cedarland
Lebanon
Lebanon...
Young girls go running around
Giggling out the door
Every generation has seen these wars before
Caught between a rock and a hard, hard place
Still you live your lives in a state of grace
Lebanon
Lebanon...
Old man smokes his pipe
And through world-weary eyes
He curses the cameras
And pleads to merciless skies
Through the ashes float the words of Khalil Gibran
Love in time will show her hand
Lebanon