What is the highness or lowness of a sound

The "highness" or "Lowness" of a sound is defined by the frequencies that conform to it.

A "sound" is conformed by the superposition of a lot of frequencies, the set of lower frequencies are the "low-pitched" part of the sound, while the higher frequencies are the "high-pitched" part of the sound.

Also, there are segments called "Mids" which refer to the mid frequencies.