A clef (from French: clef “key”) is a musical symbol used to indicate the set of pitches of written notes.
One of a group of standard symbols placed on a staff of music to indicates the range of pitches covered by that staff by identifying a standard base pitch. Examples are the treble clef (G-clef), the bass clef (F-clef), and the Middle-C clef, all of which have their own symbol.
