Tau Ceti III was an inhabited planet. It was the third planet in the Tau Ceti planetary system. This system was located in the Alpha Quadrant. This was one of four inhabited locations in this system; the others were Tau Ceti IV, Tau Ceti Prime, and Tau Alpha C.
Jean-Luc Picard first met Walker Keel at "quite an exotic" bar on Tau Ceti III. (Star Trek VI: The Undiscovered Country, production art; TNG: "Conspiracy", "Journey's End"; VOY: "Coda")
The location of Tau Ceti in "The Explored Galaxy" wall chart
The location of Tau Ceti on a star chart