The Point-to-Point Tunneling Protocol (PPTP) is one of popular VPN -  Virtual Private Network method.
 
PPTP is popular because it is easy to setup and it was the first VPN protocol that was supported by Microsoft Dial-up Networking. All releases of Microsoft Windows since Windows 95 OSR2 are bundled with a PPTP client, although they are limited to only 2 concurrent outbound connections. The Routing And Remote Access Service for Microsoft Windows contains a PPTP server.