Yadalla Prime was the main planet in the Yadalla planetary system. This planet was in the same sector as Barradas III, Calder II, and Draken IV. This sector was located near the Romulan Neutral Zone.
Yadalla Prime was the location of a Romulan archaeological site suggested as a possible raiding target for a group of mercenaries working for Arctus Baran in 2370. (TNG: "Gambit, Part I"). Starfleet Command anticipated that Baran might attack this planet so a Federation starship was sent to this planet to intercept his ship. (TNG: "Gambit, Part II")
Background
Yadalla Prime was called Yonada Prime in early drafts of the episode, a reference to the worldship in TOS: "For the World is Hollow and I Have Touched the Sky". The name was changed due to the need for Romulan origins for the planet. (Star Trek: The Next Generation Companion)
According to the Star Trek: Star Charts, on page 45, Yadalla Prime was located in the Yadalla system, in the Beta Quadrant. System primary was a Class F star. It had a magnitude of +3, which was 10 times brighter than Sol. In the ancient past, about 2,000 years ago, Yadalla was a destination on the Debrune trade route.