Enligt min musikvetenskapsbok har ordet tre meningar:
1. In Greek and medival theory, a scale of four notes spanning a perfect fourth
2. In modern theory, a set of four pitches or pitch-classes
3. In twelve-tone theory, the first four, middle four or last four notes in a row.
pitch-class - any one of the twelve notes of the chromatic scale, including it's enharmonic equivalents, in any octave
row - in twelve-tone music an ordering of all the twelve pitch-classes that is used to generate the musical
(Källa: "A History of Western Music", 7th Ed. D.J Grout, C.V. Palisca. J.P. Burkholder, W.W. Norton & Co.)
Hoppas ni förstår denna förklaring bättre än vad jag gör...