Virtual Private Network (VPN) adds the features of both public and private networks. It is fixed to single organization and needs public network for connectivity.
These connections are sometimes known tunnels and connect sites. Every site sees tunnel as point-to-point link. There is no access for other clients of public networks.
GUARANTEEING ABSOLUTE PRIVACY:
In addition to restricting data packets, VPN machines use encryption to sure absolute privacy. Even if an outside does manage to retain a copy of the data packet the outside will be unable to interpret the message.