Pocket universes are a type of very small parallel universe. They are sometimes "attached" to a larger parent universe, making them literally pockets of space, but this is not a necessary feature and the name generally refers to their small size. "Small size" can be a relative and subjective thing, however. The creation of some pocket universes might be the result of alternate timelines.
In 2377, a star-system wide bubble in space, called X-Time was created by the excess omnipotent Q-energy that Captain Daniel possessed until this moment. X-Time was created as a battle ground for omni'X to develop their powers in order to create the X Continuum. The bubble was predestined to last a full year, but inside it - time moved much slower, to that of a day. (Star Trek: Phoenix-X: "Vengeance", "Avalon Battlefield, Parts I & II")
|existence of the expanded universe|
|dimension - history - multiverse - space - space-time continuum - time - universe|
|alternate dimension - alternate timeline - parallel universe - pocket universe - subspace and hyperspace|