Quarter-tone music is a type of music that uses intervals smaller than the standard half-step found in Western music. In this system, each octave is divided into 24 equal parts, allowing for a richer variety of pitches. This approach is often used in various musical traditions, including some forms of Middle Eastern music and Indian classical music. Composers like Charles Ives and Olivier Messiaen have explored quarter-tone music in their works, creating unique soundscapes that challenge traditional harmonic structures. Instruments can be specially designed or modified to play these microtones, expanding the possibilities for musical expression and creativity.