Dry flies are designed to float or skate on the surface film and wet flies are designed to fink below the surface unless fished with a riffle hitch. For salmon and steelhead most modern dry flies use deer body hair or moose body hair to keep them bouyant and floating. Flies like the Bomber, Waller Waker, Grease Liner, Bukley Mouse, etc. are salmon/steelhead dry flies of the modern type. Flies like the various Wulff's, Elk Hair Caddis, Kaufmann's Simulator, Humpy, etc. are also dry flies suitable for salmon/steelhead when tied on light wire salmon irons (usually called low-water hooks) in sizes #2-#8.
Wet flies are the spey flies, dees flies, hair wing salmon wets like the black bear or rusty rat, steelhead hairwings like the skunk or polar shrimp, classic married featherwings, G.P.'s Irish Shrimp style flies, Ally's Shrimp, comets, burlap, spade, marabou spiders, and stonefly nymphs or glow bugs. Wets flies are to be fished under the surface from a few inches to down in the stones whether fished on a floating line or a sink tip.