The Great Rift was an astrographic feature of the galaxy. It formed one of the borders of the Outlands along with the celestial equator.
The Rebel stronghold at Yavin 4 was located in the Great Rift, and apparently Utapau as well. Yavin 4 was also located in the Forbidden Systems.
The Great Rift featured in the opening crawl in the first three drafts of the original film. In the third draft, the "Rebel strongholds" are located there, and the Imperial starfleet reaches Utapau—what would become Tatooine—as it advances toward them. It was deleted in the fourth draft. The first draft dropped the term Forbidden Systems, and re-characterized Yavin 4 as a Rebel base, thus essentially replacing the Systems with the Rift.
The Great Rift featured in the opening crawl in the first three drafts of the original film. In the third draft, the "Rebel strongholds" are located there, and the Imperial starfleet reaches Utapau—what would become Tatooine—as it advances toward them. It was deleted in the fourth draft. The first draft dropped the term Forbidden Systems, and re-characterized Yavin 4 as a Rebel base, thus essentially replacing the Systems with the Rift.