A VPN uses a public network's (PN) infrastructure to make the connections between geographically dispersed nodes, instead of using cables owned or leased exclusively for one single networks use, as is typical for a Wide Area Network (WAN). To the user, a VPN looks like a Private Network (Virtual) even though it is sharing the networking infrastructure with hundreds or even thousands of other users at the same time.
There are a variety of public networks that can be employed to make VPN connections, but the most obviously prominent and most publicly available is the Internet.