(I) A restricted-use, logical (i.e., artificial or simulated) computer network that is constructed from the system resources of a relatively public, physical (i.e., real) network (e.g., the Internet), often by using encryption (located at hosts or gateways), and often by tunneling links of the virtual network across the real network. (See: tunnel.)
Tutorial: A VPN is generally less expensive to build and operate than a dedicated real network, because the virtual network shares the cost of system resources with other users of the underlying real network. For example, if a corporation has LANs at several different sites, each connected to the Internet by a firewall, the corporation could create a VPN by using encrypted tunnels to connect from firewall to firewall across the Internet.