An SSH tunnel (sometimes referred to as a VPN") is an encrypted network tunnel created through an SSH connection. SSH is frequently used to tunnel insecure traffic over the Internet in a secure way. For example, Windows machines can share files using the SMB protocol, which is not encrypted. If you were to mount a Windows filesystem remotely through the Internet, someone snooping on the connection could see your files. To mount an SMB file system securely, one can establish an SSH tunnel that routes all SMB traffic to the fileserver inside an SSH-encrypted connection. Even though the SMB traffic itself is insecure, because it travels within an encrypted connection it becomes secure.