Virtual private network (VPN) is a network architecture for virtually extending a private network (i.e. any computer network which is not the public Internet) across one or multiple other networks which are either untrusted (as they are not controlled by the entity aiming to implement the VPN) or need to be isolated (thus making the lower network invisible or not directly usable).[1]
A VPN can extend access to a private network to users who do not have direct access to it, such as an office network allowing secure access from off-site over the Internet.[2] This is achieved by creating a link between computing devices and computer networks by the use of network tunneling protocols.
It is possible to make a VPN secure to use on top of insecure communication medium (such as the public internet) by choosing a tunneling protocol that implements encryption. This kind of VPN implementation has the benefit of reduced costs and greater flexibility, with respect to dedicated communication lines, for remote workers.[3]
The term VPN is also used to refer to VPN services which sell access to their own private networks for internet access by connecting their customers using VPN tunneling protocols.