Secure Shell, or SSH, is a protocol used to securely log in to remote servers. It's often used when you need to access a server remotely to run commands or transfer files. SSH access can be granted through an SSH key, which is a long string of characters that you create on your computer. When you're ready to log in to the server, you simply enter the key into the login prompt. The server will then check the key against its list of authorized keys and grant you access if it matches.