A mutual relation of two magnitudes of the same kind to one another in respect of quantity.
A relationship, or interval, expressing the vibrations per second, or cycles, of the two tones concerned, generally in the lowest possible [integer] terms;...simultaneously a representative of a tone and an implicit relationship to a "keynote" -- or unity.
Pertaining to ratios, such as 4/3 or 7/6.
Rational intervals are musical intervals between tones whose frequencies may be defined by ratios of whole numbers.
Irrational or tempered intervals are defined by irrational numbers.