Right off the top of my head, I would say that basically fly fishing is fishing with a fly as the attractor/bait/lure. The fly isn't heavy enough to deliver itself to the intended target, so a form of fly casting a line heavy enough to do the trick is needed. When it comes down to the rawest meaning of fly fishing, I suppose it could be done with a spinning rod, monofilament line, and a weighted bobber. There are however, as many different definitions of fly fishing as there are fly fishers. So, never mind. I'm not going to say what I just said.