Carraya IV was the inhabited fourth planet in the Carraya system. This system was located in the Carraya sector. This remote planet's location, close to Romulan space, was shown on a map from Deep Space 9 that was displayed on the bridge of the USS Enterprise-D. Carraya IV hosted several lush jungle areas and was home to the arboreal needle snake.
After being captured in a battle with Romulans, Klingon survivors from the Khitomer Massacre were brought to a secret Romulan prison camp here following the battle, and eventually learned to live in peace with their Romulan captors. The planet was not heavily fortified apart from a few Romulan soldiers. Supply ships made regular stops at the world.
The colony was kept secret until 2369, when a Yridian information dealer named Jaglom Shrek approached Lieutenant Worf with knowledge of the camp during a USS Enterprise visit to Deep Space 9. Shrek believed Worf's father, Mogh, was alive on Carraya IV, leading Worf to investigate. He found the colony and was initially held captive there, but was allowed to return to the Federation with several Klingon youths who wished to leave their secluded home. They were brought to the Enterprise aboard a Romulan Warbird, and were sworn to secrecy about the prison camp in order to protect the honor of the Klingons who remained behind. (TNG: "Birthright, Part I", "Birthright, Part II", "Rightful Heir"; DIS: "Magic to Make the Sanest Man Go Mad")
Background information Edit
"car-EYE-ah" was the pronunciation for this planet's name from the script pronunciation guide for "Birthright, Part I". 
According to the Star Trek Encyclopedia (3rd ed., p. 67), "The exterior of the prison camp was designed by Richard James, from which a model was built that was the basis for a matte painting executed by Dan Curry. (Production designer James was, of course, also responsible for the full-size interior sets, as well.)" The first edition of the Star Trek Encyclopedia (p. 43) stated that James Magdaleno was involved with the design of the prison camp too.