The term virtual private network (VPN) is widely used; in fact, it's so widely used, it means different things to different people. Let's look at the three words involved:
Virtual indicates the network topology isn't tied to a physical topology but rather a logical topology which is defined through a physical network. The network equipment used for forwarding traffic along a virtual network isn't owned or operated by the end user but rather by some service provider.
Private indicates that the security, addressing, and routing of the network (or logical topology) are completely independent of the network security, addressing, and routing of other networks running across the same physical topology.
A network is ...