It's just a flippant way of saying "hiding the URL or parameters behind running JavaScript that serves no other purpose than obfuscation". See also this commit:

https://github.com/yt-dlp/yt-dlp/commit/404f611f1c4aa516fbc4...

Of course this is easy to solve, but every layer of obfuscation they add generally requires someone to go and work around it in yt-dlp. It's mutually assured time waste on both sides.