In music, a factor or chord factor is a member or component of a chord. These are named root, third, fifth, sixth, seventh, ninth, eleventh, thirteenth, and so on, for their generic interval above the root. In harmony, the consonance and dissonance of a chord factor and a nonchord tone are distinguished, respectively.
Chord factors are taken into consideration in voicing and voice leading. A chord contains exactly as many factors as it contains unique pitch names (octaves don't matter), while a voicing can have any number of voices that draw from and represent some or all the factors of a chord in various octaves. Thus, a chord with three unique pitch names always has three factors, even if some of those pitches are doubled or omitted in a particular voicing. For example, the figure to the right shows a four-note voicing of a C Major triad, which has three chord factors. The "root" chord factor (pitch name "C"), is represented twice in the voicing by voices 1 and 4 in different octaves. The chord factor called the "fifth" (pitch name "G") is represented in voice 2 (shown in red).
In Tertian harmony, chords are made more complex, or "extended" by introducing additional chord factors stacked in thirds. The illustration shows the theoretical construction of a C13 chord having seven chord factors, with the "extended" chord factors shown in red. In real applications, it is common practice to omit the eleventh from voicings of a dominant 13 chord, because though being necessary to theoretically derive the thirteenth by stacking on it, the unaltered perfect eleventh clashes with the major third. Wikipedia, Factor (chord)