"hand-wavey" refers to (in this context) an understanding that is missing a lot of detail. The term refers to the notion that if someone asks you to explain a specific piece of the theory, you'd have to respond with "enhhhhh...." and a wave of your hand
Yep, pretty much exactly this. I understand it enough to use it as a tool and do some rudimentary troubleshooting, but to explain how it works would require some waving of the hands to fill in my knowledge gaps.
