Secure SHell (SSH) is a set of programs intended to replace and extend the functionality of the insecure "r"-programs: rlogin, rsh and rcp. It does this by employing encryption and authentication, surpassing rlogin's ".rhosts" mechanism with a secure one.
SSH encrypts all data in the connection between the local machine (the machine from which the connection is being made) and the remote machine (the machine which is being connected to). In addition to encrypting the keystrokes and screen data, SSH will also encrypt and forward X11 connections.