Elas was an inhabited planet. This was the homeworld of the Elasians, a spacefaring humanoid species. The planet was closer to its primary than its sister planet Troyius. It was located in the Tellun system. This system was located in a border area near the Federation-Klingon border.
Prior to the visit by the USS Enterprise in 2268, Federation scientists had studied the culture of the Elasians. In that year, both planets possessed the capability of mutual destruction. The wedding of the Dohlman of Elas, Elaan, to the ruler of Troyius preserved the peace.
Dilithium crystals were abundant on the planet, where it was considered to be a rather common stone. The Klingon Empire became aware of the Elasian dilithium deposits by 2268, and held the secret closely while they argued with the Federation over jurisdiction of the Tellun system. (TOS: "Elaan of Troyius")
In 2369, when shown his guest quarters aboard the USS Enterprise-D, Montgomery Scott reminisced about the time that the Dohlman of Elas was transported aboard the earlier Enterprise. He remembered her whining and complaining about the quarters. (TNG: "Relics")