What is the rainbow bridge connecting Asgard to Midgard?

The story behind the answer

Bifrost is the rainbow bridge that connects Asgard, home of the Aesir gods, to Midgard, the human world. Guarded by the ever-watchful Heimdall, it’s described in the Eddas as blazing with fire to keep out frost giants, and it will break when the forces of Ragnarök cross it.

To keep it straight: Yggdrasil is the cosmic world tree, Valhalla is Odin’s hall (not a bridge), and Vigrid (Vigriðr) is the vast battlefield of Ragnarök. Memory tip: “BI-frost