Vadris III was the inhabited third planet in its star system.

Q described Vadris as a "charming little world". The inhabitants of Vadris III believed that they were the only intelligent life in the universe. Q offered to take Vash there in 2369, but she refused. (DS9: "Q-Less")

This planet was only mentioned in dialogue.
According to the script, the pronunciation for Vadris was "van-DRIS". [1]