UPnP is a set of protocols to share media on the network. It is also supported by a wide range of residential gateways and Network Attached Storage devices. UPnP support is now commonly marketed as DLNA.
Amarok has a build in UPnP media share client so it can play tracks shared on the network. When a media share is discovered it will be shown in Local Music.
The UPnP feature depends on KDE's UPnP media server support.