Trialas IV was the fourth planet in the Trialas planetary system. This was a Class M planet near the Borderland.
When Doctor Arik Soong stole Augment embryos from Cold Station 12 in the 2130s, he fled to Trialas IV, where he raised the Augments until he was captured by Earth forces ten years later.
The Augments raised themselves until May 2154, when Malik led them in commandeering a Klingon Bird-of-Prey. They all left the planet, except for Udar, who was deemed inferior by the others. A few days later, Enterprise NX-01 visited the planet to understand more about Soong and the Augments. When the ship left, Udar went with it. (ENT: "Borderland", "Cold Station 12")
The name of the planet was not specified in the episodes, but it was given on StarTrek.com.
The scene depicting the Enterprise in orbit of Trialas IV was a reuse of Qo'noS from ENT: "Broken Bow".