Midgard is the one name in this cosmology that survived into ordinary English. Old English has middangeard, which appears in Beowulf and in Christian poetry with no pagan sense left in it, meaning simply the world people live in. Gothic has midjungards. Old Saxon and Old High German have their own forms. The word is common Germanic and older than any surviving Norse text, which suggests the idea of an enclosed middle yard is not a late poetic invention.
The enclosure is literal in the myth. Midgard is made from the body of the giant Ymir, and its defensive wall is built from his eyebrows, which places human habitation inside a fortification made out of a dismembered enemy. Outside it is Utgard, the outer yard, where the giants are. That inside and outside distinction organises much of the mythology, and it maps directly onto the Norse farm with its enclosed home field and the wild beyond.
Tolkien, a philologist by trade, took middangeard and rendered it Middle-earth, which is why the word is now attached to a twentieth century fiction in most readers' minds. He was translating rather than inventing, and the sense he kept, an inhabited middle region with older and stranger things around its edges, is the sense the Germanic sources had.