Jazz chord
Jazz chords refer to chords, chord voicings and chord symbols that jazz musicians commonly use in composition, improvisation, and harmony. In jazz chords and theory, most triads that appear in lead sheets or fake books can have sevenths added to them, using the performer's discretion and ear. For example, if a tune is in the key of C, if there is a G chord, the chord-playing performer usually "voices" this chord as G7. While in a strict classical music context, the notes of a G7 chord would be G–B–D–F, jazz often omits the fifth of the chord—and even the root if playing in a group, since the bassist will play it. Omitting the root and fifth gives the improvising chord-playing musician the option to play other notes. Also, if a seventh chord, such as G7, appears in a lead sheet or fake book, many chord-playing performers add the ninth or thirteenth to the chord, even though the lead sheet does not specify these additional notes.
Jazz players can add these additional, upper notes–seventh, ninth, eleventh, and thirteenth–because they are an important part of the jazz sound. Lead sheets and fake books often do not detail how to voice the chord because a lead sheet or fake book is only intended to provide basic guide to the harmony. An experienced "comping" performer playing electric guitar or piano adds the extra notes using their ear and taste.
In voicing jazz chords, performers focus first on the seventh and the major or minor third of the chord, with the latter indicating the chord quality, along with added chord extensions (e.g., ninths, elevenths, or thirteenths, even if not indicated in the lead sheet or fake book) to add tone "colour" to the chord. As such, a jazz guitarist or jazz piano player might "voice" a printed G chord with the notes B–E–F–A, which would be the third, sixth (thirteenth), seventh, and ninth of the chord. Jazz chord-playing musicians may also add altered chord tones (e.g., ♭9, ♯9, ♯11, ♭13) and added tones. An example of an altered dominant chord in the key of C, built on a G would be to voice the chord as "B–C♯–E–F–A♭"; this would be G7(♭9♯11).
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