Vanden Prime was the prime planet in its star system. This planet was claimed by the Cardassian Union. In 2375, the planet was used by Damar and his Cardassian Rebellion as their headquarters. (DS9: "When It Rains...")

The base, along with seventeen other rebel installations, was located and destroyed by the Dominion, weeks later. (DS9: "The Dogs of War")

The name of this planet was not spoken in dialogue but is taken from the script. In the script's list of sets, the planet was called "Avandi Prime". [1]
According to Star Trek: Star Charts (p. 46) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the Vanden system was located in the Alpha Quadrant. The system's primary was a M-class star.