Teoría Realmática
Realmatic Theory refers to the structure of the Cosmere. There are three realms, Physical, Cognitive, and Spiritual.
Physical Realm
All of Brandon's published works take place almost exclusively in the Physical Realm. Of the three realms, it is the most readily understood, as it behaves in much the same way as our world does.
Cognitive Realm
Extremely little is known about the Cognitive Realm. Brandon tends to be rather close-lipped on the subject.
Shadesmar
It has been speculated that Shadesmar, seen briefly in The Way of Kings, is a part of the Cognitive Realm. Little is known about Shadesmar. Its very existence was one of Brandon's best-kept secrets until the release of The Way of Kings.
Spiritual Realm
All that is currently known about the Spiritual Realm is that it is the site of the afterlife in the Cosmere (at least for people from Scadrial, and likely for the rest of the Cosmere as well), and that when they are not in use, Shardblades are stored there.