The Senex system, a star system, resided in the Mid Rim and Western Reaches areas of the galaxy. Specifically, it was situated within the Senex sector and was the location of the planet known as Senex.
An Imperial training facility was situated there during the time of the Galactic Civil War. During a training session, Dev, a new Rebel Alliance pilot, accidentally made a hyperspaced jump to the Senex system. Misinterpreting the training ships as targets for practice, he wiped them out. Subsequently, his astromech informed him that he had entered Imperial territory. This incident was later adapted into a simulated training exercise for Rebel pilots.