Stationary Background, Moving Foreground Website

So I have been working on a website using the .NET framework and would like to make the background style look a little something like it does at bons.me. As you can see when you scroll it background stays in the same position, however as you scroll the part of which you see changes.
Anyone know how I would go about doing this? Would it be something in css or ...? I'm rather new to web development, but it would also be just as much of a help if you guys could just point me in a direction or tell me what this is called so I could google it.