Since it seems to create a degree of controversy, perhaps it's unfortunate that the term steelhead was ever coined. In fact, the term's etymology is uncertain, it probably originated with commercial fishermen back in the day when the steelhead was still a commercial target. The steelhead has stronger, heavier bones, including its skull, than any of the other Pacific salmons and it was necessary to give it two or three whacks with the club as opposed to the one blow necessary to subdue other salmons.

As someone pointed out above, rainbow trout and steelhead are indistinguishable, even to the genetic level; resident rainbow trout can, and do, produce migratory offspring and migratory rainbows (steelhead) can, and do, produce resident offspring. Most rainbows exhibit some form of migratory behavior where it is possible; be it moving from a small stream down to a larger one, from a stream to a lake or, where accessible, to the ocean in order to feed and grow before returning to their natal streams to spawn.

As Roderick L. Haig-Brown wrote: "The rainbow is an individualist, a pioneer searching always wider scope; mere rivers confine him and he goes with the salmon into the breadth of the sea, to grow himself to the silvered nobility of the steelhead".