Subspace

Subspace is an exotic area of space that has different physical properties from normal spacetime and follows new laws of physics. Generating a subspace field can alter the mass of an object, which breaks the old laws of physics. It can also be used for communications over vast distances as all particles travel faster than light, and exist beyond the Planck scale.

Subspace has 3 dimensions which have u, v and w axes independent to the axes of lower dimensions that work with the traditional or old laws of physics. Using these dimensions 9, 10 and 11, it is possible to access or create pocket universes or conduits that lead in and out of higher dimensions. These 3 dimensions can be used in multiple combinations with themselves or lower dimensions to create multidimensions or higher, or subspacetime for instances.

Subspace is chaotic, in that a child u-v-w matrix can inherit all characteristics of a parent space, but all laws of physics within the child space are strange; for example matter can be created or destroyed, information lost, and c is the minimum speed. It requires extremely advanced science to be able to move between parent and child space via conduits and still remain intact on entry or exit.

Black (and white) holes contain singularities that break the laws of physics and subspace conduits into other dimensions. A wormhole can also link two points of a universe (or beyond) via subspace.

Subspace may also be used to breach reality into other realms like the Afterlife.

Trivia:
The Borg used transwarp conduits (similar to wormholes) which they created through an area of subspace known as transwarp space. They were used to cover great distances in which a Borg vessel could reach velocities at least twenty times greater than the maximum warp speed of a Federation starship.