That is not the definition at all. If I kept track of my passwords by making them the first letter of each page of various books on my bookshelves, that would be security through obscurity, because, while if someone who broke into my home knew about my system, it would be quite easy to extract all my passwords, but if they didn't know about my system, they would be looking forever for a notebook with cryptic letters in it, or sticky notes on the monitor, etc.