tolkiens legendarium - Is Middle-Earth a time, or is it a place?

I was looking at the map of Middle-Earth and it made me wonder. Does Middle-Earth refer to the time frame in which the LOTR stories took place, or does it refer to the area in which the LOTR tales unfold? To help clarify what I'm asking: Is the rest of Tolkiens' unmapped world Middle-Earth too, or is Middle-Earth the era?

Answer

Middle-earth is the name for the parts of the world in Tolkien's universe where men lived. It was based on the Old English/Norse term "Middangeard" as used, for example, in Beowulf. The term "middle" here comes from the Norse idea of nine connected worlds, of which men lived on the one in the center. This distinguishes Middle-earth from, for example, Valinor where the immortal Valar lived.

Tolkien's Middle-earth includes other places that are not on his maps of Middle-earth that are still part of that region, but there are also unmapped areas that are outside of Middle-earth. Tolkien described Middle-earth as basically being surrounded on all sides by ocean, so anything that was "across the seas" would be somewhere else.

In practice, Tolkien fans often just use "Middle-earth" to mean the setting of the novels, without being too concerned with where it stops and starts