how do you define impressionism in music?

[bonjing]

I just started playing piano and I heard this piece by debussy which is clair de lune. My friend told me that it's one of the impressionist piece from debussy. My thought about it is it's very dramatic and emotions. I would love to learn more about impressionism.

[communist]

It is meant to almost as "background music", I.E. to make a formal setting.