What is SSH?

SSH or Secure SHELL is an authentication protocol that support several authentication methods. (Certificate based, username/password)

But we have telnet?

Remember what I told you about Telnet in this article? Yes indeed, it sends all packets in clear-text over the wire and thus is a big security risk.

This is where the SSH protocol shines. It does not send any packets in clear-text. Everything is encrypted and thus only visible/available to the sender and the receiver.