Setlik III was the formerly inhabited third planet in the Setlik system, in the Alpha Quadrant. This system was near to the Federation-Cardassian border. Prior to 2347, a Federation outpost had been established on this planet.
During the Federation-Cardassian War, the planet was the target of a sneak attack by a squad of the Cardassian military, which resulted in close to a hundred civilians killed, including the family of Benjamin Maxwell, in what became known as the Setlik III massacre. The USS Rutledge was the first Federation starship to respond, though largely too late to prevent the deaths. (TNG: "The Wounded"; DS9: "Emissary")
Miles O'Brien became known as the "Hero of Setlik III" for leading a successful attack against the Cardassian Barrica encampment during that action. (DS9: "Empok Nor") O'Brien also managed to repair a field transporter under combat conditions to allow himself and thirteen others to escape the planet's surface. (DS9: "Paradise")
During the battle of Setlik III, Starfleet officer Raymond Boone was captured and killed and then replaced by a Cardassian spy who continued to serve in Starfleet until discharged in 2362. Commander Benjamin Sisko exposed 'Boone' as a Cardassian spy in 2370. (DS9: "Tribunal")
In 2367, Glinn Daro acknowledged that the attack on Setlik III had been "a terrible mistake", as the Cardassians had erroneously believed it to have been the staging ground for a massive Federation attack. (TNG: "The Wounded")
This planet was only mentioned in dialogue.
According to the script for "Emissary", the pronunciation for Setlik was "SET-lik".