Comma
From XenReference
Comma is typically a small interval that, in a temperament, defines the logarithmic difference (division) between two other intervals which are assigned to the same approximate interval. For example: in meantone temperament, the syntonic comma, 81/80, is result of dividing four justly tuned perfect fifths (3/2)4 and two octaves plus a justly tuned major third 4/1 × 5/4.
