The Rashirmir is also known as the Barrier, or the Dream Realm. It is the space that exists between all other realms and protects them from each other. The Sect of the Dream Realm is devoted to the understanding of the Rashirmir.
The Rashirmir is also said to act as a conduit to other realms, most notably the four Elemental Realms. When Mages call upon those elements, they channel power that passes through the Rashirmir.