What does it mean to be stupid?

Gevlon has an interesting post about being a mercenary in WoW. Even more interesting to me is that in it, he claims a very specific breakdown of capable players to morons. Not surprisingly, he declares most people to be morons.

This is nothing new, lots of people accuse the majority of the rest of the population of being idiots. People even arbitrarily declare made up statistics (like I'm assuming Gevlon did), such as "90% of people are stupid." While a part of me agrees with this sentiment, the scientific, rational part of me wants to know "what does it mean to be stupid?"

There is a joke about a dog playing checkers. An onlooker says, "I can't believe how smart that dog is!" To which the owner replies, "he's not smart, I've beaten him 8 times in a row." The joke is based on the relativism of what it means to be "smart." For dogs, the standards are different. Most dogs cannot play checkers, so being able to play the game at all would constitute a dog being "smart." No one would think a dog who could not play checkers was "stupid."

This gives us a way to view what is "smart" and what is "stupid," simply by using the majority as "typical." If 90% of humans in incapable of understanding a certain thought process, that does not make them stupid. That makes it something which humans typically cannot do, and the 10% who can are smart for humans.