System J-25 was a planetary system that had at least six planets, located outside Federation space. As of 2365, the nearest Federation starbase to this system was Starbase 185; a Galaxy-class starship would require two years and seven months to reach it from J-25.
The sixth planet was class M and previously inhabited by an intelligent species, who were ultimately destroyed by the Borg.
In 2365, the Borg still had a presence in the system. A Borg cube detected the Federation starship USS Enterprise-D when it was transported to this system by Q in 2365. Shortly afterward, the cube attacked the Enterprise and pursued it across the system before the Starfleet vessel was rescued by Q.
Guinan was familiar with the area of space in which System J-25 was located, as her people had explored it in the past. (TNG: "Q Who")
