A virtual private network (VPN) is an overlay network. It is a logical network established on top of a physical, usually public, network and may span several geographical regions
VPNs differ in their architecture and transport protocols used to establish the overlay network. The VPN architecture may be either point-to-site site-to-site.
Point-to-siteVPN
To provide a device with remote access to a private network.
Site-to-site VPN
Used to establish an imaginary bridge between two private networks as if they were connected directly.
The transport connection established between two VPN entities is usually called a tunnel and the process of routing traffic through that tunnel is called tunneling.