Veloz Prime was the inhabited prime planet in its star system. This system was located in the Demilitarized Zone.

The planet was the site of a former Cardassian colony. In 2373, the Maquis, led by Michael Eddington, detonated three stratospheric torpedoes laden with cobalt diselenide in Veloz Prime's atmosphere. The nerve agent spread across the planet, forcing the Cardassians to evacuate. The Maquis settled the planet shortly after. (DS9: "For the Uniform")

This planet was only mentioned in dialogue.
According to the script, the pronunciation for Veloz was "VEL-loze". [1]
According to Star Trek: Star Charts (p. 46) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the Veloz system was located in the Alpha Quadrant. This was a binary system with a K-class star and a F-class star.