Final answer:
Pitch is the term used to describe the frequency of sound waves and is determined by the tension of the vocal folds, controlling the highness or lowness of a sound.
Step-by-step explanation:
The frequency of sound waves is known as pitch, which is determined by the tension on the vocal folds. When the muscles of the larynx relax or tighten, they change the tension on the vocal cords, which in turn alters the pitch of the sound. The frequency is the number of sound waves that pass a point in one second, measured in hertz (Hz). Higher frequency sounds have a higher pitch, and conversely, lower frequency sounds have a lower pitch. This concept extends to all animals, with different species capable of hearing different ranges of frequency.