Acronym for Point-to-Point Tunneling Protocol

A technology for creating Virtual Private Networks (VPNs) , developed jointly by MicrosoftCorporation, U.S. Robotics, and several remote access vendor companies, known collectively as the PPTP Forum. A VPN is a private network of computers that uses the public Internet to connect some nodes. Because the Internet is essentially an open network, the Point-to-Point Tunneling Protocol (PPTP) is used to ensure that messages transmitted from one VPN node to another are "secure". With PPTP, users can dial in to their corporate network via the Internet.

If you want to support this under Linux, get PoPToP. It starts a pppd in the correct place; you might be interested in the MPPE patches.