A powerful and rare magic, rifts are the openings – seemingly torn right into the air – that allow the magic user to step from one location to another at some distance. Rift-users must be powerful in order to hold that gap open; it’s been likened to lifting a huge, heavy stage curtain and holding it up as one walks beneath.
Some magic users, like His official titles are Prince of Umbra, Lord of Crows, Echelon of Darkness, and Heir to the Darkseed, and he... More, are able to jump between worlds with rifts, but it’s such a rare skill that some magical philosophers believe it to be a different skill entirely.
There are some who believe creating rifts destabilizes the world in which they are made, though at such a slow rate that this is mostly a theoretical concern. Mostly.
Note: rift-makers are distinct from world-walkers, who are able to travel from world to world without tearing holes.