equal temperament

noun, Music.
1.
the division of an octave into 12 equal semitones, as in the tuning of a piano.
Encyclopedia Article for equal temperament

in music, a tuning system in which the octave is divided into 12 semitones of equal size. Because it enables keyboard instruments to play in all keys with minimal flaws in intonation, equal temperament replaced earlier tuning systems that were based on acoustically pure intervals, that is, intervals that occur naturally in the overtone series. For a more technical explanation of overtones, see sound: Standing waves

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