Claude Debussy was a child prodigy, much like Mozart. His talent made such an impression that he was taught by a student of Frederick Chopin, himself taught music to the children of Tchaikovsky's patron, and was enrolled in the Paris Conservatory when he was only 11. By the 1880s, he was hanging out in Montmartre with the impressionist crowd. Impressed by the avant garde idea that art should appeal to the senses (rather than the intellect), he wrote a series of tone poems that are perhaps best described as "lush".
Clair de Lune means "Moonlight" in French. Debussy wrote a tone poem inspired by Paul Verlaine's 1890 poem of the same name:
The scene in Ocean's Eleven where the gang watch the Bellagio Fountains while this song plays is very well done, and follows the spirit of Verlain's poem - especially at the end, just before the song finishes, where the fountains let off one last mighty roar and then fall silent. A very subtle tip of the hat in a very well done film.
Your soul is as a moonlit landscape fair,
Peopled with maskers delicate and dim,
That play on lutes and dance and have an air
Of being sad in their fantastic trim.
The while they celebrate in minor strain
Triumphant love, effective enterprise,
They have an air of knowing all is vain,—
And through the quiet moonlight their songs rise,
The melancholy moonlight, sweet and lone,
That makes to dream the birds upon the tree,
And in their polished basins of white stone
The fountains tall to sob with ecstasy.
But that's looking at things through the prism of the intellect, not the senses. This song is so incredibly well known (it's been used in maybe 120 different films) precisely because it speaks in the voice of emotions. Speaks to the right brain, not the left. To the soul, not the mind.
This piece is seductive in its initial and ending simplicity, and can inspire someone to attempt to learn the piano. The middle of the piece is an entirely different matter, with rapid rolling arpeggios reminiscent of his later piece La Mer. Easy to start, hard to master.
This piece has a special meaning for me, capturing a particular instant of my life. Hearing the opening bars is enough to take me back to a particular bittersweet time and place, of melancholy moonlight and dreams that you know are in vain. Where the future was painted in flecks of color that you were still too close to be able to make out the picture. A tone poem, indeed.