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).
I am the toiler the old ship-slave
I stoke the fire that keep you brave
And this I gave for all mankind
to sail away on an ocean wave..
I am the voyager of the ocean grey
I wayfarer see fairway
And this I gave for all mankind
to sail away on an ocean wave..
I am the sailor - the ocean slave
Fill your sail with the breath I gave
And this I gave for all mankind
to sail away on an ocean wave..
I am the captain of the love brigade
With every breath I am your slave
And this I gave for all mankind
to sail away on an ocean wave..
..sail away on an ocean wave
..sail away on the airwaves