The Ghost Nebula represented both a nebula and a sector, situated within the Slice region of the Expansion Region. This nebula acted as a barrier, obscuring the light emanating from the majority of stars located behind it and within its boundaries, thus causing its isolation from the larger galaxy, a factor that contributed to its evocative name. The nebula's core contained massive stars emitting ultraviolet radiation, which ionized the gases in the vicinity, generating plasma that enveloped the planets within the nebula with ultraviolet light. It encompassed the inhabited planets Umbara and Atoa, the original homeworlds of the near-Humans known as the Umbaran and Atoan races, respectively.
During the period of the Clone Wars, this nebula held strategic importance as a crucial, albeit isolated, supply corridor. In this context, the Galactic Republic engaged in conflict with the Confederate-supporting Umbaran militia to secure dominion over their native planet. Following the establishment of the Galactic Empire, the Atoan system was subjugated after an unsuccessful uprising spearheaded by the disloyal Garoche Tarkin alongside local resistance fighters.