Clef (noun)

1. A symbol placed at the beginning of a staff in music notation to indicate the pitch of the written notes.
2. A sign or symbol used to indicate the pitch of written music.

Origin:

From old french clef, from latin clavis ("key").

Examples:

1. The treble clef is used for the higher pitched instruments.
2. The bass clef is used for the lower pitched instruments.
3. The clef at the beginning of the staff helps to indicate the pitch of the notes.
4. The musician sight-read the piece with ease, thanks to the clef changes.
5. The clef is an important symbol in music notation.