SSH is an acronym for Secure SHell, a remote command-line access mechanism. It’s refered to as “secure” because all comminications are encrypted. SSH is most commonly available on Linux and other Unix-derived systems. It is used to access the equivalent of a Windows Command Prompt.
SSH is also unique in that it supports an additional form of authentication based on public-key encryption and can be configured to require that only those in possession of the proper encryption key will be allowed access.