I think many people,including me are miss understanding the meaning of “fly fishing”,And here is the information i found to explain the mean of fly fishing
As wikipedia said:Fly fishing is an angling method in which an artificial "fly" is used to catch fish. The fly is cast using a fly rod, reel, and specialized weighted line. Casting a nearly weightless fly or "lure" requires casting techniques significantly different from other forms of casting. Fly fishermen use hand tied flies that resemble natural invertebrates or other food organisms, or "lures" to provoke the fish to strike.
Fly fishing can be done in fresh or salt water. North Americans usually distinguish freshwater fishing between cold-water species (trout, salmon, steelhead) and warm-water species, notably bass. In Britain, where natural water temperatures vary less, the distinction is between game fishing for trout or salmon and coarse fishing for other species. Techniques for fly fishing also differ with habitat (lakes and ponds, small streams, large rivers, bays and estuarys, and open ocean.)
I still confused about this definition for the “fly fishing”, so i am go ahead and find other information about fly fishing
Fly fishing is most renowned as a method for catching trout, grayling and salmon, but it is also used for a wide variety of species including pike, bass, panfish, and carp, as well as marine species, such as redfish, snook, tarpon, bonefish and striped bass. Many fly anglers catch unintended species such as chub, bream and rudd while fishing for 'main target' species such as trout. A growing population of anglers attempt to catch as many different species as possible with the fly. With the advancement of technology and development of stronger rods and reels, larger predatory saltwater species such as wahoo, tuna, marlin and sharks have become target species on fly. Realistically any fish can be targeted and captured on fly as long as the main food source is effectively replicated by the fly itself and suitable gear is used.