Interval Class (i.c.) -- The distance between two pitch classes. The identity, or size, of an interval expressed as a number of semitones without regard to (1) spelling, (2) octave compounding, or (3) inversion; the minor third C-natural4 -E-flat4, the major sixth E-flat4 - C-natural5, and the minor tenth C-natural4 - E-flat5 are all members of the same interval class