The relationship between the first note and the second note in a chromatic scale (or any two adjacent chromatic notes). It is also the inversion of the major seventh. A minor second in just intonation corresponds to a pitch ratio of 16/15 or approximately 1:1.0666, while in equal temperament tuning it is a ratio of 1:21/12 (approximately 1.059). It’s also defined as 100 cents.

