jackofallgeeks | Beta Readers?

I've heard the term before, usually as a verb in Miss Leslie's vocabulary ("I was going to have her Beta my fic first"), but I was wondering if one might explain to me what a Beta Reader is.

Tangentially, I was wondering if any of you out there would be interested in helping me out with some feedback on my story, likely as I write (and rewrite) it. I was thinking of setting up a mailing list that I could send my novella-in-progress out on, and get something of a stream of feedback in return, telling what's good, what doesn't work, what they think of the story, and how they think they'd like to see it progress. I'm really getting more of a concrete idea of what i'm doing with my story -- I even have something of a starting place to jump off of and get my Protagonist into It All -- the piece I've been missing all summer. But I'm sure I can't find all the flaws and redundancies in my story, and so I need ~~wordmonkeys~~ Beta Readers (or something) to help me out.

Or something. Any takers?