(1) The communications media that join two network nodes together. A subnetwork is a representation within the OSI reference model of a real network, such as a carrier network, a private network, or a local area network (LAN).
(2) A distinct partitioned piece of an internet network represented by two or more sets of addresses that are subsets of the network's range of addresses.
(3) A configuration whereby a single IP network address is split up so it can be used on several interconnected local networks. A subnetwork is a local configuration; outside it appears as a single IP network.