System J-25 was a star system. The system had at least six planets. Far outside Federation space, at maximum warp of a Galaxy-class starship, it was more than two years and seven months from the closest starbase, Starbase 185. It was in a sector of the galaxy familiar to El-Aurians, but unexplored by the Federation.
The Federation starship USS Enterprise-D was transported 7,000 light years to this system by Q in 2365. Scans revealed evidence of an advanced civilization on one of the planets, but also massive surface scarring notably similar to that detected on several Federation and Romulan outposts along the Romulan Neutral Zone in 2364, which had removed all machine elements on the planet. Shortly after, the Enterprise-D made First Contact with a Borg cube in the outskirts of the system, which was likely responsible for the destruction on the surface. Guinan was familiar with the area of space in which System J-25 was located. (TNG: "Q Who")