A grouping of systems forming a chain of worlds
all reachable by jump-1. This grouping
provides a sort of "corridor" allowing jump-1 capable ships to travel to
any world along the chain without ever exceeding jump-1.
Many such groupings of worlds exist in the Imperium. Prominent examples include
the Spinward Main in the Spinward Marches, the Vilani Main centered in the Vland sector, the Sylean Main in Core Sector, and the
Antares Main originating in the Antares sector.