Stupidity is a word which is generally used to mean low intelligence. However, it has other, more specialized definitions which may be more appropriate to LessWrong's goals:

Carlo Maria Cipolla defines stupidity as the tendency to commit acts that damage others while not benefiting, or even harming, oneself.
A common definition of stupidity is "doing the same thing over and over again, while expecting different results".
According to Robert J. Sternberg, stupidity is widespread in politics, despite the fact that politicians generally have quite high intelligence.

Contrast: winning

Blog posts

I'm Not Saying People Are Stupid by Eliezer Yudkowsky