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 the notes of a G7 chord are G–B–D–F, jazz often omits the fifth of the chord—and even the root if playing in a group. However, not all jazz pianists leave out the root when they play voicings: Bud Powell, one of the best-known of the bebop pianists, and Horace Silver, whose quintet included many of jazz's biggest names from the 1950s to the 1970s, included the root note in their voicings.
Improvising chord-playing musicians who omit the root and fifth are given the option to play other notes. For example, if a seventh chord, such as G7, appears in a lead sheet or fake book, many chord-playing performers add the ninth, thirteenth or other notes to the chord, even though the lead sheet does not specify these additional notes. Jazz players can add these additional, upper notes because they can create 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 may add or remove notes as chosen according to the style and desired sound of that musician, but must do so in a way that still emphasizes the correct musical context for other musicians and listeners.
In voicing jazz chords while in a group setting, 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 G7 chord with the notes B–E–F–A, which would be the third, sixth (thirteenth), flat 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).