Defiant Core was a base established on Innton II, a planet near the Triton system. It had been built out of a previous Separatist base that had been made using parts salvaged parts from a Recusant-class light destroyer, Nova Defiant, that had crashed on the planet. The Separatists were not able to finish the construction before the end of the Clone Wars and left it abandoned. Later the Alliance to Restore the Republic found the base largely intact after investigating rumors of its existence. The Rebels housed a squadron of Y-wing starfighters at the base and was under command of General Romar Kek.[1]
Sources
Outer Rim and Defiant Core on Fantasy Flight Games' official website (backup link)- Strongholds of Resistance