The Mists

General
Before there were humans or dwarves, before there were even worlds or the stars that light the night sky, there was but one thing in the universe-- the Mists. The mists touch all things. They are what binds the universe together, past present and future. They are the source of all good and evil, and all matter and knowledge. It is said that all forms of life, no matter how simple or complex, can trace their origins back to this one place.

The Mists contain and connect the mortal worlds and The Rift, the worlds of the immortal gods and spirits.

Some immortal beings are apparently able to travel directly through the mist to step over from one world to the other, while mortal beings have to use special portals, such as the one located in The Tomb of Primeval Kings.

Trivia
The Mists seem to be similar to what æther (the "5th element") is in classical alchemy, natural philosophy, and - in modified form - in religion and esoterics.

The mists is where World PvP will take place in the upcoming GW2.

The ritualist hero Razah is from the mists.