They are things that your browser happily rebroadcasts back to the server with no real UI for it outside of the shitty devtool bar made for devs, even after all this outcry about cookies.
It reminds me of the meme of the guy riding a bicycle, throwing a branch into the spokes (rebroadcasting cookies), and then roaring in pain on the ground about how evil websites/advertisers are tracking him with cookies.
That said, what a lame HN thread on a post about Haskell.