A clef is a musical symbol that indicates the pitch of each line and space on a musical staff. It is placed at the beginning of the staff, and it determines the absolute pitch of the notes that are written on the staff. There are three clefs in common use today: the treble clef, the bass clef, and the alto clef. The treble clef is used for high-pitched instruments such as the violin and the flute. The bass clef is used for low-pitched instruments such as the cello and the tuba. The alto clef is used for instruments that are in between the treble and bass clefs, such as the viola and the clarinet.