The ordering of files in the `/etc/ssh/sshd_config.d/` directory is crucial for SSH (secure shell) configurations. The first-defined rule dictates that configuration settings defined earlier in the order take precedence over later definitions. This is particularly relevant in scenarios where user-defined configurations could override admin settings, especially for SSH clients. A user has shared a comprehensive breakdown of SSHD (SSH daemon) and SSH options, illustrating how they can be organized and executed based on file naming conventions and order. They also emphasize the importance of careful management of configurations to ensure security and functionality, rather than relying on default templates provided by VPS hosts, which may lead to vulnerabilities.