12-tone equal temperament is a musical tuning system that divides an octave into 12 equal parts, known as semitones. This allows for consistent intervals between notes, making it easier to play in different keys without retuning instruments. This system is widely used in Western music and is the foundation for most modern instruments, including the piano and guitar. By using 12-tone equal temperament, composers and musicians can create harmonies and melodies that sound pleasing across various musical styles.