The starling comma or septimal semicomma, 126/125 (about 13.8 cents), is the superparticular 7-limit comma which is the difference between 36/35 (septimal quartertone) and 50/49 (jubilisma). In terms of just intervals, it is the amount by which 12/7 falls short of three 6/5 minor thirds. It is also the amount by which two 5/3 major sixths (octave-reduced, 25/18) fall short of the 7/5 tritone, and the amount by which three 5/3's (octave-reduced) fall short of the 7/6 septimal minor third. It can also be found when comparing the conventional 5-limit minor third and major tenth to the nearest Bohlen–Pierce intervals.
Tempering it out alone in the 7-limit leads to the starling temperament, and enables starling chords. See Starling family for the rank-3 temperament family where it is tempered out. See starling temperaments for a collection of rank-2 temperaments where it is tempered out.