IQ is

Intellectual Disability (ID), formerly known as Mental retardation. ID is defined as a disability characterised by significant limitations in both intellectual functioning and in adaptive behaviour that emerges before the age of 18 years. Wide acceptance of this definition has led to the international consensus that an assesment of both social adaptation and intelligenc quotient (IQ)are necessary to determine the level of intellectual disability. Ref: Synopsis of Psychiatry, 11e, pg 1118