Say you're on this page:

As you scroll down the page, the map follows you to be at the top of the web browser within the sidebar.

What is that effect called, or anyone have a link explaining it? I'm guessing it's javascript.

I've tried searching for it, but aye, no luck so far. I'd like to impelment something similar on a site I'm working on, even if not as fluid as Yelp's example.