Outpost 23 was a Federation station along the Romulan Neutral Zone. In 2367, it was the key outpost in Starfleet's defenses along the border.
During a fantasy created for William T. Riker's benefit by Barash on Alpha Onias III, Outpost 23 was supposedly no longer of strategic importance and was slated to be the site of final peace negotiations between the Federation and the Romulan Star Empire, an apparent ruse to reveal the location of the outpost. (TNG: "Future Imperfect")