The original NaNoWriMo is a "contest" of sorts to challenge yourself to write 50,000 words in a month (November, to be precise). Well, originally it was to write a novel in a month, but 50,000 words is nowhere near the length of a novel, so I'm not sure that's exactly relevant anymore.

Camp NaNoWriMo is a spin-off of the original that happens in May and July. The participant can choose their own word-count goal, but the default is still 50,000 words.

Maybe the original intention was to create this for amateur writers, but I've met professional writers in the process and I know some at least do the November contest. It's a good chance to meet writers (amateur, professional, and of all ages) and bounce ideas off of each other, support each other, etc.

If one doesn't wish to associate with amateur or unpublished writers, then this probably isn't the thing for you.