A Clef is a musical symbol placed at the beginning of the stave to indicate the pitch of a written note. There are 4 main clefs. The clef used is chosen dependent on the instrument that the music is written for. The word clef directly translates into the word key in French, hence the name.
Clefs are very useful in music and without them you wouldn't know which octave to play in. If a bass instrument like a tuba would to read music and it was in the treble clef, the tuba player would find it very difficult to read lots of ledger lines (see ledger lines section). However, if it was in the bass clef the tuba player would find it easy to read the notes as they would all be on the stave.
Click on the buttons below to see the different types of clefs!