Starbase 25-Alpha was a Federation starbase in operation in the late 24th century. Unlike other Federation outposts, Starbase 25-Alpha wasn't listed in fleet installation guides due to the fact that it was used by Starfleet as a secret installation that was involved with advanced technology development, munitions manufacture and communications interception.
The USS Enterprise-E traveled to the station, along with her mirror universe duplicate ISS Enterprise-E, after the two ships had engaged in a pitched battle. After arriving at the station, both starships underwent repairs and Commandant Jean-Luc Picard and the crew of the mirror Enterprise were taken into custody. (Star Trek novel: Preserver)