The term GFC is an acronym for the three musical clefs: G (treble), F (bass) and C (alto). These clefs are used to indicate the pitch of notes on a musical staff. The treble clef is used for higher pitched instruments such as the violin, while the bass clef is used for lower pitched instruments such as the cello. The alto clef is used for middle-pitched instruments such as the viola. Together, these three clefs provide a comprehensive system for notating music.