Musical notation symbol at the beginning of a staff to indicate the pitch of the notes on the staff. Clefs were originally letters, identifying letter-named pitches, that were affixed to one or more of the staff's lines (thus providing a key to their identity). Knowing the identity of a single line permitted the musician to identify all the other lines and spaces above and below. Clefs were first regularly used in the 12th century. The Gothic letter forms of G and F evolved into the modern treble and bass clefs, respectively; the letter C evolved into the rarer alto, tenor, baritone, and soprano clefs.