The Paulson Nebula was a nebula located in Federation space, between Zeta Alpha II and Sentinel Minor IV. It was comprised of 82% dilithium hydroxyls, magnesium, and chromium, elements which served to block sensors, making the region a navigational hazard.
In 2366, the USS Enterprise-D used the Paulson Nebula to hide from a pursuing Borg cube. While the strategy was temporarily effective, the Borg eventually launched magnetometric guided charges into the nebula, forcing the Enterprise out. (TNG episode: "The Best of Both Worlds")
Following the Borg Invasion of 2381, Lieutenant Dina Elfiki of the USS Enterprise-E suggested that survivors of the attack might have taken refuge in the Paulson Nebula, and were possibly still in hiding there weeks later. (TNG novel: Losing the Peace)
During the Klingon-Federation war in 2409 the Klingons used the nebula and nearby system Lackey to establish a hidden listening post. The Gorn, who were allies with Klingons at the time, set up an illegal mining operation in the nebula to extract dilithium. (STO video game: Star Trek Online)