Comma

A comma is typically a small interval that, in a temperament, defines the (logarithmic) difference between two other intervals which are assigned to the same approximate interval. For example, the syntonic comma, 81/80, is the difference between the diatonic major third and classical major third, and is tempered out in meantone, which equates them. A comma can be contrasted with a diesis, which is usually understood to not be tempered out.