microexpression

n. An extremely brief facial expression of emotion, often appearing for only a fraction of a second. These were originally discovered by the psychologist Paul Ekman as a sign of concealed or repressed emotions. Microexpressions are often, but not always, associated with deception, although there are many times in which microexpressions occur because of concealed feelings that are not necessarily lies. Contemporary work with microexpressions has shown that there are reliable individual differences in the ability to see microexpressions, and that the ability to see them can be systematically trained.