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. Jouret IV, one of the outermost colonies of the Federation, was located over 7,000 light years away.

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", "The Best of Both Worlds")

After the Borg incident, Commander William Riker wrote reports about the event and what was learned from surveys of the system and its planets. These reports became known to Shelby who was tasked with the Borg tactical analysis six months before the Battle of Wolf 359. (TNG: "The Best of Both Worlds")

According to Star Trek: Star Charts (p. 13) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), System J-25 (FGC-J25) was located in the Beta Quadrant. The system's primary was an A-class star. This system was located near the Borg transwarp network.
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