SSH: SEALING THE PIPES
SSH, for the uninitiated, is a program that's used to log into another computer over a network, run programs on a remote system and move files between computers. Providing strong authentication and secure transmission over open channels (like the Internet), Secure Shell replaces less-secure terminal programs, such as telnet and rsh.
The only way a Unix sysadmin could not know about SSH is if he's been hibernating for the past six years or so. The first thing many admins do upon completing a Unix, Linux or BSD installation is replace telnet and r-utilities (rsh, rcp, etc.) with SSH.