An intellectual disability is defined by the American Association on Intellectual and Developmental Disabilities as "significant limitations in both intellectual functioning and in adaptive behavior." These limitations affect everyday social interactions and basic life skills and must be present before the age of 18.
Intelligence functioning is essentially general intelligence which is comprised of the ability to learn, retain information, solve problems, and use reasoning and logic skills.
Adaptive behaviors are skills that are learned in daily life and from interactions with the environment and other people. These included basic social skills, learning, and the behaviors that occur in day to day life. Someone with an intellectual disability can have difficulty with these behaviors due to their condition.