Polychord
In music and music theory, a bichord or polychord consists of two or more chords, one on top of the other. In shorthand they are written with the top chord above a line and the bottom chord below, for example F above C: 
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The use of polychords may suggest bitonality or polytonality. Harmonic parallelism may suggest bichords.
Examples may be found in Igor Stravinsky's Petrushka, p. 15, and Rite of Spring, "Dance of the Adolescents" (1921) (see Petrushka chord). They may also be found in the song "Point of No Return" from Andrew Lloyd Webber's The Phantom of the Opera, including chords such as E♭m over Fm.
In the polychords in the image above, the 1st, "might well suggest," a thirteenth chord, the 2nd may suggest a, "d minor ninth chord with upper extensions," but the octave separation of the 3rd makes the suggestion of, "two independent triads with their a m9 apart," even more likely, and the 4th is a, "split-third chord."
Extended chords contain more than one triad, and so can be regarded as a type of polychord:
Podcasts:
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by Billy Sherwood
Comfortably Numb
by: Billy SherwoodHello.
Is there anybody in there?
Just nod if you can hear me.
Is there anyone home?
Come on, now.
I hear youre feeling down.
Well I can ease your pain,
Get you on your feet again.
Relax.
I need some information first.
Just the basic facts:
Can you show me where it hurts?
There is no pain, you are receding.
A distant ships smoke on the horizon.
You are only coming through in waves.
Your lips move but I cant hear what youre sayin.
When I was a child I had a fever.
My hands felt just like two balloons.
Now I got that feeling once again.
I cant explain, you would not understand.
This is not how I am.
I have become comfortably numb.
Just a little pinprick. [ping]
Therell be no more --aaaaaahhhhh!
But you may feel a little sick.
Can you stand up?
I do believe its working. good.
Thatll keep you going for the show.
Come on its time to go.
There is no pain, you are receding.
A distant ships smoke on the horizon.
You are only coming through in waves.
Your lips move but I cant hear what youre sayin.
When I was a child I caught a fleeting glimpse,
Out of the corner of my eye.
I turned to look but it was gone.
I cannot put my finger on it now.
The child is grown, the dream is gone.