Like the Emerald Dream, the Shadowlands are tangentially linked to the world of Azeroth. Yet whereas the Emerald Dream represents life, the Shadowlands represent death. They are nightmarish realms of decay, labyrinthine spiritual planes teeming with the souls of the dead who have passed from the world of the living.
The origins of the Shadowlands remain uncertain, but they have existed ever since mortal life first arose in the physical universe. Many believe that mortal souls are drawn into this dark place at the point of death, where they remain forever after. Still others hope that their souls will go to a brighter place, rather than languish for eternity within the cold confines of the Shadowlands.
- the World of Warcraft Chronicle Vol. I on the Shadowlands