I remember that definition from high school. It's funny how useless that definition is, in that, knowing it doesn't help you figure out what it really is.<p>The newer definition: "In 1983, the metre was redefined as the distance travelled by light in free space in 1⁄299,792,458 of a second." always kind of bothered me because it sounds like it went like this:<p>"Ok, so we defined the speed of light as 299,792,458m/s and it's all over textbooks and formulas, but the thing is that our current definition of a meter sounds a little bit like a guess. So let's just reverse the speed of light and we're good!" It feels like a backronym to me (<a href="http://en.wikipedia.org/wiki/Backronym" rel="nofollow">http://en.wikipedia.org/wiki/Backronym</a>)