Network discovery is not a single thing. In general terms it is the process of gathering information about the Network resources near you. It consists of a group of protocols that all report to the Function Discovery platform. Probably the most well-known protocol is NetBIOS Browsing, but it also includes WSD, UPNP, SSDP, and even the registry. Typically you see this information in Network Resources/Network Neighborhood, but any application can potentially be programmed to use it.