System J-25 was a star system with at least one M-class planet, located 7,000 light years from Federation space.

The Federation starship USS Enterprise-D was transported to this system by Q in 2365. Scans revealed evidence of a previous advanced civilization on the planet, 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 made first contact with a Borg cube in the outskirts of the system, which was likely responsible for the destruction on the surface. (TNG: "Q Who")

Guinan was familiar with the area of space in which System J-25 was located.