The following is adapted from information provided by the ARC of the United States
Intellectual disability is a below-average cognitive ability with three (3) characteristics:
Intelligent quotient (or I.Q.) is between 70-75 or below
Significant limitations in adaptive behaviors (the ability to adapt and carry on everyday life activities such as self-care, socializing, communicating, etc.)
The onset of the disability occurs before age 18.
Intelligence refers to general mental capability and involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly, and learn from experience.
Sometimes intellectual disability is also referred to as developmental disability which is a broader term that includes ASD (autism spectrum disorders), epilepsy, cerebral palsy, developmental delay, fetal alcohol syndrome (or FASD) and other disorders that occur during the developmental period (birth to age 18).