Interstellar asteroid visited by Discovery in 2257
An interstellar asteroid was an asteroid found in interstellar space, rather than in orbit of a star.
During the Federation-Klingon War, the USS Hiawatha crash landed on an interstellar asteroid in enemy space. Ten months later, after the war, USS Discovery came upon the asteroid while investigating a red burst originating from it, and captured a fragment of it. (DIS: "Brother")