A chord chart (or chart) is a form of musical notation that in addition to writing out non-embellished melody, describes harmonic and rhythmic information. It is the most common form of notation used by professional session musicians playing jazz or popular music. It is intended primarily for a rhythm section (usually consisting of piano, guitar, drums and bass). In these genres the musicians are expected to be able to improvise the actual notes used to represent the chord and the appropriate ornamentation or counter melody.
The harmony is given as a series of chord symbols above a traditional musical staff. The rhythmic information can be very specific and written using a form of traditional notation, sometimes called rhythmic notation, or it can be completely unspecified using slash notation, allowing the musician to fill the bar any way he sees fit (called "comping"). In Nashville notation the key is left unspecified by substituting numbers for chord names.
Slash notation is a form of purposefully vague musical notation which indicates or requires that an accompaniment player or players create their own rhythm pattern or comp according to the chord symbol given above the staff. On the staff a slash is placed on each beat (so that there are four slashes per measure in 4/4 time).
Slash notation and rhythmic notation may both be used in the same piece, for example, with the more specific rhythmic notation used in a section where the horn section is playing a specific melody or rhythmic figure that the pianist must support, and with slash notation written for the pianist for use underneath improvised soli.
Nashville notation or Nashville number system is a method of writing, or sketching out, musical ideas, using numbers in place of chord names. For example, in the key of C major, the chord D minor 7 can be written as "dm7", "2m7", or "ii7".
In the key of C, C=1, D=2, E=3, and so on for
all seven notes in the key. So, the chord
Nashville notation, while
in the key of G would also become
This method of notation allows musicians who are familiar with basic music theory to play the same song in any key.