For the Star Trek: Voyager episode of the same name, please see "Coda".
A coda was the final passage of a musical composition.
In 2367, Jenna D'Sora fretted over her flute performance, saying that as a result of becoming confused over the phrasing, she had ruined the piece's coda by breathing at the wrong times. Data assured her that the audience had not noticed. (TNG: "In Theory")