Stupid is an adjective meaning lacking in intelligence.
Stupidity (also called fatuity) is the property a person, action or belief instantiates by virtue of having or being indicative of low intelligence or poor learning abilities. Stupidity is distinct from irrationality because stupidity denotes an incapability or unwillingness to properly consider the relevant information. It is frequently used as a pejorative, and consequently has a negative connotation. The term has fallen out of favor in medical journals as it is seen as a generic term used to describe a wide variety of conditions.
In psychology, group stupidity is known as deindividuation in crowds, and can lead to behaviors usually not displayed outside the specific social situation. The behaviors are attributed to a variety of causes, including loss of self-identity, incentives to conform to group behavior, and other dynamics.
