A Singular overlay output is a keyable HTML layer that sits on top of your video. Many streaming/production software out there supports adding browser/webpage layers to combine your Singular overlays with your video to stream live.
Overlays or graphics of the past are passive and burned into video. Singular overlays (websites) live on a separate layer, over your video, and don't have to be burned into your video. This allows you to generate more advanced overlays with features such as interactivity, device adaptivity and overlays that can be always be live, updated and changed.