Pocket Dimensions

Pocket Dimensions are sub-universes that are interconnected to a main Realm or Dimension. The number of pocket dimensions per universe vary, although each tend to have at least one sub-universe that can be breached or interacted in some shape or form.

Overview
A Pocket Dimension is invariable, meaning the size, scope, and number of any given Pocket Dimension for a universe isn't set in stone. In fact, it may change on a day to day basis, or even worse. Nevertheless, the domain is forever tethered to the it's parent universe. Thus if the parent universe were to somehow cease to exist, so would the pocket realm.

Storage Dimensions
These dimensions are inherent to almost all the Realms. In simple terms, a Storage Dimensions is where common sealing techniques store a particular object, or entity. For example, the basic sealing technique, stores all of the inanimate objects in the Human World's variant of the Storage Dimension. In theory, if one could access it, they'd have the ability to pillage or steal items from the dimension without anyone knowing.

Prison Dimensions
These are dimensions crafted by powerful fuuinjutsu practitioners, or powerful clerics in most cases. The pocket dimensions are typically designed especially to imprison an despicably powerful entity or presence, and thus is tailor made to suppress their power and potential to escape.

Other
These types of pocket dimension range in use - with the bulk coming into existence as a result of special, space-time techniques.