In the context of Special Olympics, the term "intellectual disabilities" is a synonym for mental retardation. Therefore, Special Olympics uses the definition of intellectual disabilities/mental retardation provided by the World Health Organization (WHO), the United Nations' specialized agency for health. According to the WHO, intellectual disability is a condition of arrested or incomplete development of the mind characterized by impairment of skills and overall intelligence in areas such as cognition, language and motor and social abilities. Intellectual disabilities can occur with or without any other physical or mental disorders. Although reduced level of intellectual functioning is the characteristic feature of this disorder, the diagnosis is made only if it is associated with a diminished ability to adapt to the daily demands of the normal social environment.

A person is considered to have an intellectual disability for purposes of determining his or her eligibility to participate in Special Olympics if that person satisfies any one of the following requirements:

• The person has been identified by an agency or professional as having an intellectual disability as determined by their localities; or
• The person has a cognitive delay, as determined by standardized measures such as intelligent quotient or "IQ" testing or other measures that are generally accepted within the professional community in that Accredited Program's nation as being a reliable measurement of the existence of a cognitive delay; or
• The person has a closely related developmental disability. A "closely related developmental disability" means having functional limitations in both general learning (such as IQ) and in adaptive skills (such as in recreation, work, independent living, self-direction or self-care). However, persons whose functional limitations are based solely on a physical, behavioral, or emotional disability, or a specific learning or sensory disability, are not eligible to participate as Special Olympics athletes, but may be eligible to volunteer for Special Olympics as partners in Unified Sports®, if they otherwise meet the separate eligibility requirements for participation in Unified Sports set forth in the Sports Rules.