Pitch class is a term used in modern music theory for all notess which have the same name; for example, all Es, no matter which octave they are in, are in the same pitch class.

The term is often used in reference to serial music and the twelve-tone technique, which regulates the pitch class of notes but not their octave. In this case, because of enharmonic equivalency, it is more accurate to say that a pitch class is all of octaves of a pitch, which would be labeled by a number, not a traditional letter name.

In both cases, when "pitch class" is used, the use of "pitch" indicates a specific frequency or note and does not include its octaves.