So this whole "is a wave energy, or is it a form of energy", I think depends on the following: Is a "wave" what the wave is made out of; water waves are "made out of water", right? Is a "wave" what propagates in a medium, in which case it's not the medium but a state of the medium? I think that argument was settled way back in this thread. (but, this is sciforums) Water waves depend on water as they propagate, but the waves aren't the medium; in some sense they map a medium to itself, something like how a purely mathematical function can map a domain to itself. And I really think the claim "energy is not stuff", should be amended to "energy is not measurable stuff, but it is physical".