Elas was an inhabited planet, the inner of the two, the other being Troyius, found within the Tellun system in the Alpha Quadrant. This was the homeworld of the Elasians, a spacefaring humanoid species.
In 2256, this planet was mentioned with the star system's name on the star chart "Alpha/Beta Quadrant Overview" in the ready room aboard the USS Discovery. (DIS: "Magic to Make the Sanest Man Go Mad")
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 by Ensign Kane, Montgomery Scott reminisced to him 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")
In 2399, this planet was mentioned with the star system's name on a Federation star chart that was in Fleet Admiral Kirsten Clancy's office at Starfleet Headquarters. The system was in or near Federation space. (PIC: "Maps and Legends")