SSH (Secure Shell) is a network protocol for encrypted remote administration. It replaces insecure protocols such as Telnet and offers, besides the command line, secure file transfer (SCP, SFTP) and port forwarding. Authentication typically uses key pairs, which is more secure than passwords. You should disable root login via SSH, enforce key-based authentication, and change the default port. In an ISMS, SSH is part of the controls for secure administration and remote access. Ensure regular key renewal and disable legacy cipher suites.