The examples web page (which is otherwise helpful, although quite hard to find) has "Undefined" headings for all of the example commands after #5. They do have detailed explanations, so I'm not sure if this is intenional or not.
https://exiftool.org/examples.html
That we page isn't linked from any of the documentation because it was never finished.
However, you're the second one to be confused by this in the past couple of months, so I have put an "under construction" notice on that page.
- Phil
I was going crazy trying to find that first post before I thought that it wasn't posted here in the forums.
It was posted on github (https://github.com/exiftool/exiftool/issues/172).