retardation, mental

n. Significantly slowed or delayed intellectual development, which results in limitations in adaptive functioning, usually defined as having an IQ more than two standard deviations below average. Mild retardation is the IQ range about 50–55 to 70, depending on the IQ test used. Moderate retardation is the IQ range 35–40 to 50–55. Severe mental retardation is the IQ range 20–25 to 35–40. Profound mental retardation is the IQ range below 20 or 25. Also called developmental delay.