It's pronounced "ensemble" by the way. And, one way that a pianist would have a role would be by being in the background as an example and playing his part. He's going to play what he needs to play. The question does seem a little to vague, but truly, I would say simply, that the person who is playing it, just plays his part as they all make music sound good.
I’m bot completely sure, but since there is minimal shadowing, I would say the technique is contouring
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Abstract art is art that is know for the shapes and colors it uses. And it's know to not be realistic and just be whatever the artist decides.
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