We used to call it “hair brush” internally, and I still like this name. It is a video matting tool that keeps the details when separating complicated foreground elements like frizzy hair or motion-blurred edges from complex backgrounds. This means you can create natural-looking composites without keying specially shot footage. When combined with Roto Brush we developed earlier, they give you a powerful, brand new workflow for rotoscoping.
Watch the demonstration here.