A term that has been used in contemporary music theory to describe the tone is pitch class. The term pitch class indicates a notion of pitch in which its class is definable, given the principle of octave equivalence. For instance, the pitch class "C" refers to the tone "C", regardless of its octave (or height). Similarly for all 12 tones in an octave. It is by virtue of the notion of pitch-class that we can specify the name of a tone without specifying its particular octave.