Portal Rift

Dimensional rifts are holes in reality, generally, this game is talking about gate rifts, which are Links between places that serve as a "Shortcut".

How to Make a Rift
There are three known ways to make a rift: Magic, Psionics and gravitational distortion.

Rift Worlds
All  Rift Worlds contain at least three rifts, hence their name. These appear to be natural phenomenon, at least as natural as the worlds themselves...