The Orelious system was a star system.
In the 14th century, Orelious IX was the location for the Battle of Orelious IX, a decisive battle between the Promellians and the Menthars in which they fought to their mutual extinction. The planet was destroyed in the course of the battle.
In 2366, the Federation starship USS Enterprise-D charted the battlefield and discovered the Promellian battle cruiser Cleponji. (TNG: "Booby Trap")
"oar-LEE-us" was the pronunciation for this system from the script pronunciation guide;  however, according to Startrek.com, the pronunciation for Orelious was "oh-REE-lee-us".