A term used to define disability under the Americans with Disabilities Act of 1990 (ADA), as amended by the Americans with Disabilities Act Amendments Act of 2008 (ADAAA). One way an individual is recognized as having a disability under the ADA is if the individual has a physical or mental impairment that substantially limits one or more major life activities.

The ADAAA and its implementing regulations changed the ADA's definition of substantially limits, but did not set out a precise new definition. Instead, the regulations provide nine rules of construction to help employers assess whether an impairment substantially limits a major life activity. For more information on these rules of construction, see Practice Note, Disability Accommodation Under the ADA: Definition of Substantially Limits and Disability Definition Under the ADA and ADAAA Comparison Chart.