The term C, F and G are all musical clefs. A clef is a symbol used in musical notation to indicate the pitch of written notes. The three clefs most commonly used in modern music notation are the treble clef (G), bass clef (F) and alto clef (C). The treble clef is used for higher pitched instruments such as the violin, flute, and saxophone. The bass clef is used for lower pitched instruments such as the cello, trombone, and bassoon. The alto clef is used for middle-pitched instruments such as the viola.