The Spinward Rim is a region in space in the Ancient universe. CRON, Terra, Xeen, and Enroth were all located within the Spinward Rim.
Webstation Beta-5 was constructed by the Ancients to allow people to travel within the region, and to other regions in the Web of Worlds, but when the kreegans infiltrated the web, the Spinward Rim was cut off from the rest of the web - an event later known as the Silence.