A sarcophagus was a type of coffin.
In the 23rd century, the Klingon Great house of Girjah were known to craft sarcophagi for members of their family. T'Kuvma then took them aboard the Sarcophagus where he laid them upon the ship's hull as parts of the Black Fleet. T'Kuvma would continue to build sarcophagi for his followers such as Rejac in 2256. (DSC - The Light of Kahless comics: "Issue 1", "Issue 3"; DSC episode: "The Vulcan Hello")