Interesting. Your definition takes into account both the length of the flight and the location (indoors or outdoors). Mine is more focused on the location and the substance (wood, concrete, etc) than the size, although I think even if it's indoors and made of wood I would call a single one a step. I think I would say, "I had to walk up the first two stairs before I could reach the lightswitch." But if we're talking about down to the basement, "I had to walk down the first two steps before I could reach the lightswitch." I wonder why that is -- maybe because it's not living-space? See, this is why I asked in the first place, because otherwise I never would have learned that about my own language habits!