D-Jump device
From Jenny Everywhere Wiki
A D-Jump device was a device used to shift between universes by people with no inherent shifting powers. It took the form of a handheld, tube-shaped device which, when activated, would create a temporary, circular, shimmering blue portal that could then be stepped through.
The Man With No Name used a Mark II D-Jump device to travel the Multiverse, and stated in 2009 that it had been “out of date since 2005” when he, Red Max and Jenny Everywhere discovered a more advanced variant in use by the Brotherhood of Multiversal Oneness. (COMIC: The Legend of Jenny Everywhere)
Behind the scenes
“D-Jump” presumably stands for “dimension-jump”, although this is not made explicit in The Legend of Jenny Everywhere.