Using apt list --installed I got a list of installed packages. I have plenty of time and wanted to go through the list and see what's what. Are they all executable? I see that accountsservice is the first one on the list, but it's not executable as far as I can see. It just returns command not found. Third on the list is adduser, and that is executable. I know that's a standalone command too.
Are some of them system applications that can only be called by the OS and cannot actually be executed individually?