Tau Ceti III was an inhabited third planet orbiting the star Tau Ceti. This planet was located proximately eight light years from Earth. (TNG: "The Naked Now", production art)
Prior to stardate 41775, Jean-Luc Picard first met Walker Keel at "quite an exotic" bar on Tau Ceti III. (TNG: "Conspiracy")
"tow (rhymes with cow)- set-ee 3" was the pronunciation for Tau Ceti III from the script pronunciation guide.