Multi-Verse, sometimes written multi-verse or MultiVerse and occasionally abbreviated 'verse', is short for "multiple universes" and describes the Course Books storyworld. The Consecution and Antelope series' take place within the same storyworld. However, the many worlds across which the story takes place (originally divided by the Roads War) cannot be accurately described as "universes" in the conventional sense, in that having more than one pretty much negates the term "universe".
Each "universe" or dimension is separated by walls of aether which cannot be physically crossed. People and machines can cross between worlds by magic, or by a variety of technologies, but cannot simply walk or fly from one world to another.
The Course Books primarily take place within a segment of the verse called "the Known Worlds", covered mostly by the Alliance and Gudersnipe Foundation. The unknown beyond this is believed to be relatively small by comparison, but the true extent of the Multi-Verse is not fully understood. The Antelope Books take place on a planet just beyond the Known Worlds, but within charted territory.
The fourth and fifth books of the series involve an invasion from another Multi-Verse, thus offering the theory of multiple Multi-Verses. Joshua later offers that the aether walls surrounding "their" Multi-Verse are simply very thick, and proffers that it is all really one Multi-Verse subdivided by thicker-than-normal aether walls, creating "clusters" of improperly-defined universes. With this knowledge, how far the Empire of Roads truly stretched remains a mystery.