Which term refers to the highness or lowness of a sound?

The term that refers to the highness or lowness of a sound is pitch. Pitch is a fundamental characteristic of sound, determined by the frequency of sound waves; higher frequencies produce higher pitches, while lower frequencies result in lower pitches. Understanding pitch is crucial in music as it helps singers and musicians identify notes and harmonize effectively.

While time signature, measure, and rest are important musical concepts, they pertain to different aspects of music. The time signature denotes the number of beats in a measure and the note value that receives one beat. A measure is a segment of time defined by a given number of beats, contributing to the rhythm of a piece of music. A rest represents a period of silence in a piece of music. None of these concepts directly relate to the quality of sound in terms of its highness or lowness, making pitch the correct answer.