This page functions as a mini "glossary" of VPN terms. It contains basic terminology and concepts, and the protocols commonly used by VPNs.

Note: You do not need to understand every item on this page in order to set up or use a VPN — the majority of providers offer simple setup instructions. However, it's always good to have some understanding of the terminology surrounding VPNs.
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VPNA VPN (Virtual Private Network) is simply a network of computers connected over the Internet. With a commercial VPN provider, users' traffic is encrypted and tunnelled through the VPN, preventing eavesdropping or surveillance, and allowing anonymous and private browsing and downloading of content. The use of VPNs as a means of maintaining digital privacy has increased exponentially in recent years.
ISPAn ISP (Internet Service Provider) is a business which offers access to the Internet. All Internet users access the Internet through an ISP. Popular ISPs include Comcast, Verizon, and AT&T in the United States; Sky, BT, and TalkTalk in the United Kingdom, and Linkem, Tiscali, and BT Italia in Italy.
OpenVPNOpenVPN is software which allows a user to connect to a VPN. OpenVPN is very popular, and many VPN providers use it. Most providers offer guides or tutorials for setting up or troubleshooting OpenVPN connections. It is available on Windows, Mac OS X, Linux, as well as devices running Android 4.0+, iOS 3GS+, and others.
L2TP/IPsecL2TP/IPsec is a VPN protocol. Data sent using P2TP/IPsec is encrypted. Supported by Windows, Mac OS X and Linux.
PPTPPPTP (Point-to-Point Tunnelling Protocol) is another protocol for VPN connections. PPTP does not necessarily require data to be encrypted. It is supported by Windows, Linux, and Mac OS X and offered by many VPN providers.

Due to known, serious security flaws in Windows' implementation of PPTP, and other security concerns, it is recommended to instead use OpenVPN or L2TP/IPSec if available.
SSL (TLS) SSL (Secure Sockets Layer) is a protocol which allows secure, encrypted Internet communication. TLS (Transport Layer Security) is a newer protocol, based on SSL. Most people use SSL/TLS on a daily basis, without realising it: https uses SSL to encrypt data, preventing traffic snooping. Most banks and online shops use https to protect their customers' sensitive data, such as their credit card information.
P2PPeer-to-peer refers to a network with no central server; individual users ("peers") transfer content to each other. Popular P2P software includes BitTorrent. By design, BitTorrent shares the IP address of peers, so BitTorrent users often turn to VPNs to stay anonymous and prevent traffic throttling by their ISP, or prevent legal action by copyright holders or rights groups.