Root SSH means using the Secure Shell (SSH) service to log into a device with root, or full administrative, privileges. SSH normally provides encrypted remote command-line access, but when it runs as root, the session can change system files, inspect secrets, install tools, and alter security controls.
In cyber security, root SSH is important because it often marks total post-exploitation control. Attackers use it after a jailbreak, exploit, or stolen credential to persist on a system and move deeper into its configuration. Defenders look for unusual SSH exposure, forced recovery states, unexpected key changes, and privileged logins on devices that should not offer remote admin access. If root SSH appears where it is not expected, it is a strong sign that the trust boundary has already been crossed.