UPnP (Universal Plug and Play) - definition
UPnP is a set of networking protocols among network enabled devices which allows devices (such as computer, mobile, printer, devices) discovers the presence of each other in the same network and establish an secure connection and operate with each other meaninglessly. i.e.: If you have a printer in the house and it is automatically recognized by the devices like mobile, laptop and others and act accordingly, then you’re UPnP connected.