The neutral or percussion clef is not a clef in the same sense that the F, C, and G clefs are. It is simply a convention that indicates that the lines and spaces of the stave are each assigned to a percussion instrument with no precise pitch.
ith the exception of some common drum-kit and marching percussion layouts, the keying of lines and spaces to instruments is not standardized, so a legend or indications above the stave are necessary to indicate what is to be played. Percussion instruments with identifiable pitches do not use the neutral clef, and timpani (notated in bass clef) and mallet percussion (noted in treble clef or on a grand stave) are usually notated on different staves than unpitched percussion.
Staves with a neutral clef do not always have five lines. Commonly, percussion staves only have one line, although other configurations can be used.
The neutral clef is sometimes used when non-percussion instruments play non-pitched extended techniques, such as hitting the body of a violin, violoncello or acoustic guitar, or when a vocal choir is instructed to clap, stomp, or snap, but more often the rhythms are written with X marks in the instrument's normal stave with a comment placed above as to the appropriate rhythmic action.