Western, Educated, Industrialized, Rich, And Democratic
WEIRD is an acronym used to remind scientists, particularly experimental psychologists, that the majority of published studies are performed on a very specific demographic: most often college students, but more generally, people living in industrialized, democratic, and Western societies, and generally only on those rich enough to have free time to spend in psychological experiments. This is a far cry from studying 'humans' as a class.
This was perhaps most strongly advertised after a 2008 survey of psychology journals1 found that 68% of all study participants were from the US and 96% from Western industrialized nations (i.e., Europe, North America, Australia, and Israel). However,
it has also been noted that studies outside of psychology might be affected by bias in Western BMI, height, diet, and medical profile.
1. Arnett, J. 2008. The neglected 95%: Why American psychology needs to become less American. American Psychologist 63(7): 602-14.