Because it actually does mean something, even if we don’t really know what and borders are fuzzy.
When you hear that X is more intelligent than Y, there is some information you learn, even though you didn’t find out exactly what can X do that Y can’t.
Note that we also use words like “mass” and “gravity” and “probability”; even though we know lots about each, it’s not at all clear what they are (or, like in the case of probability, there are conflicting opinions).
r/Fitness does a weekly "Moronic Monday", a judgment-free thread where people can ask questions that they would ordinarily feel embarrassed for not knowing the answer to. I thought this seemed like a useful thing to have here - after all, the concepts discussed on LessWrong are probably at least a little harder to grasp than those of weightlifting. Plus, I have a few stupid questions of my own, so it doesn't seem unreasonable that other people might as well.