a condition, usually present from birth, characterized by intellectual functioning that is below average: it ranges in degree from borderline (IQ of 71-84) to mild (IQ of 50-55 to approximately 70) to moderate (IQ of 35-40 to 50-55) to severe (IQ of 20-25 to 35-40) to profound (IQ of below 20-25): this technical classification has replaced the older terms moron, imbecile, and idiot