Chronicles of Time
Pocket Dimensions are tiny planes that exist between other planes. Sometimes even are weaved into the holes of planes. Pocket Dimensions are usually not very large and can be created magically.
Pocket Dimensions can be extremely hard to locate, and can exist within any of the levels of planes, though the rarest are found in folds of Elemental planes.
In all rights though, the Pocket Dimension is its own plane free of the rule of others. Some Pocket planes are unstable however, and can be dangerous. If a pocket plane collapses, it is likely to kill any mortals within.