Great, now you can start putting your customizations in that directory instead of the OS-managed /etc/ssh/sshd_config blob. That's why the `.d/` convention exists.
I had to look up the info because I wasn't sure really, so I appreciate the direct question. It means 'directory' or 'conf.d pattern'. So you have your config file, and the config directory that contains "parts" of the config to be merged with the main one to provide customizations/overrides.
