SSH is a widely used protocol for system administration and file transfer. In addition, it has a feature called SSH tunnelling  (or SSH port forwarding). It creates an encrypted connection between a local computer and a remote computer through which you can relay traffic. It is very useful, and you can use it to securely access unencrypted protocols such as VNC or firewalled resources like database servers. You can also use it as a form of proxy/VPN and get around restrictive, firewalled networks.
