A canon was a musical composition technique in which different performers began playing/singing the same melody with a temporal offset.
Two Earth songs that used the technique were "Frère Jacques" and "Row, Row, Row Your Boat". (TNG: "Lessons", "Disaster"; Star Trek V: The Final Frontier; TNG: "Hero Worship")
In 2259, Nyota Uhura and Spock sang an improvised canon while discovering that the systems of M'hanit responded to musical input. (SNW: "Strange New Worlds")
