The Solais system was an independent star system.
In 2365, the Federation starship USS Enterprise-D ferried a mediator to Solais V. He was there to negotiate a peace to a centuries long planetary conflict. (TNG: "Loud As A Whisper")
In 2371, the SS Xhosa ferried cargo to Solais V. (DS9: "The Adversary")
"so-LAY-is" was the pronunciation for this system's name from the script pronunciation guide.