Quarter Tone

A quarter tone is an interval about half as wide as a semitone

Quarter tone is a musical term that refers to the microtonal interval that lies halfway between a semitone and a whole tone, often referred to as half a semitone. In Western classical music, quarter tones are rarely used, but they are widely used in some world music, modern music, and experimental music. Traditional instruments such as the piano and guitar are not capable of producing quarter tones, but some instruments, such as certain string and woodwind instruments from the Middle East, are capable of playing quarter tones.

Example of Quarter Tone

How Many Notes Are There? The Theory of Quarter Tones