In legal terms

What is the definition of disability under the ADA?

It is important to remember that in the context of the ADA, “disability” is a legal term rather than a medical one. Because it has a legal definition, the ADA’s definition of disability is different from how disability is defined under some other laws, such as for Social Security Disability related benefits.
The ADA defines a person with a disability as a person who has a physical or mental impairment that substantially limits one or more major life activity. This includes people who have a record of such an impairment, even if they do not currently have a disability. It also includes individuals who do not have a disability but are regarded as having a disability. The ADA also makes it unlawful to discriminate against a person based on that person’s association with a person with a disability.