Bifrost
The Bilröst, anglisied as Bifrost and also known as the Rainbow Bridge, is a form of long-range teleportation utilised by the Aesir.
(Due to its name, it is often confused with the bridge connecting Valaskjalf to the Himinbjörg. The bridge is made of bifa crystals, which act as anchor points for the magic powering the Bifrost, and which refract light, creating the impression of a bridge made of rainbows, hence the confusion.)
Dr Jane Foster, the pre-eminent Midgardian expert on the subject, theorises that the Bifrost is in fact an Einstein-Rosen bridge, a type of previously theoretical wormhole. However, the Bifrost is powered, in large part, by magic, making any scientific study of it extremely challenging.
The Bifrost is guarded and opperated by the Gatekeeper of Asgard, a possition which has been held by Heimdall since early in Odin's reign. While others can opperate the bridge, provided they possess the Bifrost Sword, Heimdall's gift of vision makes him the most qualified of the Aesir to guard and opperate the bridge.
Utility
Access to the Bifrost is strictly controlled, due to the potential dangers. If any part of a person is outside the energy field when the Bifrost activates, it can result in extreme injuries, amputation, or even death.
In addition, if opperated by someone who does not possess the gift of far-sight, there is a risk of the destination being unsafe, such as landing in the middle of the ocean, landing somewhere with no exit, or even landing on top of or inside another living creature.
Manufacturing
The Bifrost was first constructed during the reign of Bor. It was constructed by a team of expert engineers from accross the Nine Realms, including Vanir and Light Elven sorcerors, Dwarven engineers, and Mountain Giant minerologists.