What it is rep power, and how does it work?

[companioncube]

Im came here an hour ago, and I noticed in the sidebar to the left that there is something called rep power. I've seen some people who have gained several hundreds! I was just wondering how that system works. Is it user-voted, or automatically calculate based on lists? What is it?

EDIT: sorry! Should've read the stickies. Ahh. Found my into there. Sorry