In its broadest sense, the head of a piece of music is its main theme, particularly in jazz, where the term takes on a more specific set of innovation . In other types of music, "head" may refer to the first or most prominent section of a song. The term may, though obtusely, be applied to classical music, insofar as classical pieces generally bear similar thematic elements, but the preferred term in this instance is (main) theme or subject. The term "head" is most often used in jazz and may refer to the thematic melody, an instance of it in a performance of the song, or a more abstract compilation of ideas as to what the song is. It may also, though uncommonly, refer to the first section of the melody, or the theme riff in the melody.
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There is a slightly related musical direction, D.C. or da capo (Italian, from head), which means to go back to the very beginning of the sheet music and play to the end, typically ignoring all repeat signs.