Ferris VI was the inhabited sixth planet in its system. The planet was featured in the Massacre of Ferris VI holo-program available at Quark's Bar.
For their double date, Nog suggested that he and Jake Sisko might take their dates to a holodeck suite where they could relive the massacre, and loot and pillage villagers. (DS9: "Life Support")
This planet was only mentioned in dialogue.
It was never stated outright if Ferris VI was a real or fictional location.