Midgard is one of the nine worlds connected by Bifröst,the rainbow bridge that runs through Yggdrasil. Midgard was the world where humans populated earth.
Ragnarök[]
It is said that all humans on Midgard will be wiped out by Ragnarök except a man named Liftraser and a woman named Lif who found shelter in Yggdrasil. In the myth they would re-populate Midgard.