The United Nations Convention on the Rights of Persons with Disabilities defines disability as including: long-term physical, mental, intellectual or sensory impairments which in interaction with various barriers may hinder [a person's] full and effective participation in society on an equal basis with others.

The Americans with Disabilities Act defines a person with a disability as one who “has a physical or mental impairment that substantially limits one or more major life activities, a person who has a history or record of such an impairment, or a person who is perceived by others as having such an impairment.”

Disabilities often occur for the following reasons: Genetic mutations (changes) Having an extra or missing chromosome Exposure to alcohol, tobacco, drugs, and certain infections while in the womb Childbirth complications, such as being born prematurely or not receiving enough oxygen during birth Injury to the brain or spinal cord