This is an article about a VPN protocol. For more information about available protocols, please refer to this article: https://support.nordvpn.com/hc/en-us/articles/206931809-Choosing-between-VPN-protocols
OpenVPN is an open source VPN protocol that executes virtual private network (VPN) techniques for producing safe site-to-site or point-to-point connections in remote access facilities and bridged or routed configurations. OpenVPN uses a custom security protocol which utilizes TLS/SSL for key exchange. It is able to traverse firewalls and network address translators (NATs). James Yonan wrote it and published it under the GNU General Public License (GPL).
OpenVPN allows peers to authenticate each other using username and password, certificates, or a pre-shared secret key. When used in a multi-client server configuration, it allows the server to launch an authentication certificate for every user using certificate authority and signature. It uses the OpenSSL encryption library broadly as well as TLSv1/SSLv3 protocols and consists of many control and security features.