SSH stands for Secure Shell.
Accessing and using the remote machines (i.e, for execution of commands) are performed by connecting to the remote machine by using Telnet, rlogin application. Such applications are not secured hence the data's exchanged can be interrupted by the network peers. One such alternative to this mode of communication is Secure Shell. Secure shell encrypts the data sent between the systems and makes it secured.
It supports Public key authentication for user authentication.