Clef
Octave clefs
Tenor banjo is commonly notated in treble clef. However, notation varies between the written pitch sounding an octave lower (as in guitar music and called octave pitch in most tenor banjo methods) and music sounding at the written pitch (called actual pitch). An attempt has been made to use a treble clef with a diagonal line through the upper half of the clef to indicate octave pitch, but this is not always used.
Neutral clef
If the neutral clef is used for a single percussion instrument the staff may only have one line, although other configurations are used.
History
Before the advent of clefs, the reference line of a staff was simply labeled with the name of the note it was intended to bear: F, C, or sometimes G. These were the most common 'clefs', or litterae clavis (key-letters), in Gregorian chant notation. Over time the shapes of these letters became stylised, leading to their current versions.