What is “Secure Shell” (SSH)?

Secure Shell (SSH) is a protocol used for securely connecting two computers.

A terminal client can use SSH to connect to (and control) another computer or device, like a smartphone or e-reader or cable box or any other computer or computer-like device that can be accessed via SSH.

SSH can also be used by FTP clients in order to move files between computers.

(You can login to another computer using a username and password. But ideally, you should what is called an SSH key.)