Mistuning

In music mistuning is most generally the action of incorrectly tuning or the state of being out of tune. Mistuning is also the displacement of a pitch a semitone away from its standard position in a stable tonal structure such as the most common perfect fourth or fifth, which mistuned in the opposite directions produce a tritone. A portion of the alpha chord:E-G-C-E♭, may be considered an E major chord: E-G♯-B-E, whose members are mistuned. (Wilson 1992, p.9) See alteration and chord substitution.