The WebGUI is a mini webserver and websocket server. Most people are familiar with what a web server can do. Web servers take requests and server content. Typically, they do not allow allow full duplex communication over a long period of time. Websocket do allow this behavior. One large benefit of this, is web pages can start behaving like complex applications. "Refreshing" a page to get new information is no longer required.
Those are the 2 protocols the WebGUI offers, it also has 2 interfaces.