VPN

VPN
Virtual Private Network. A data network that uses the Internet rather than leased lines for connections. Security is guaranteed by means of a tunnel connection in which the entire information packet (content and header) is encrypted an encapsulated.

This is a "virtual" network constructed by connecting computers together over the Internet and encrypting their communications so that other people cannot understand the communications. The benefit is that people can connect to the LAN from anywhere on the Internet. This allows easier connectivity and lower phone bills for travelling salespeople. They just sign up with a national ISP and call local POPs from their hotels as they travel the country and easily connect back to their company's local network. Microsoft's answer to VPNs is PPTP. See also PPTP 

Windows NT, 2000 and XP offer native VPN support. Also, VPNs are recommended to secure 802.11b wireless LANs as well.