meantone

In music, a tuning system which was a common technique used for keyboard instruments before equal temperament came into general use. It provided for the pure intonation of the key of C major and those lying near it at the expense of the more extreme sharp and flat keys, which is the reason why remote keys were rarely used in keyboard works, before the adoption of equal temperament. There was, for example, a pure F sharp and B flat, but these notes were out of tune when used as G flat or A sharp.