I imagine word usage varies across fields. As someone whose background is in quantum field theory, I can tell you we use the word "light" pretty much indiscriminately to refer to light of all wavelengths, from the AU-scale (e.g. Hawking radiation from supermassive black holes) all the way to gamma rays -- incidentally, what I call a gamma ray, and what I've always seen called gamma rays, is light with energy per photon on the order of 0.1 MeV or above. But I'm aware that there are fields whose practitioners would call such light "x-rays" if its source is, say, bremsstrahlung, rather than nuclear processes. At any rate, I found the descriptions in the quotes adequate. Infrared radiation behaves very similar to visible light is, I think, the important takeaway.Those are terrible quotes/explanations, both I would say are *jast plain wrong*. EMR is *not* typically known as light, nor should it be, as most of it is not light, as it's not in the visible range. And the "optical" radiation spectrum *is* the "visible* spectrum.