Final answer:
An individual is substantially limited in performing a major life activity when their ability to carry out essential everyday tasks is significantly restricted due to a physical or mental impairment, as addressed by the Americans with Disabilities Act (ADA).
Step-by-step explanation:
When an individual is said to be substantially limited in performing a major life activity, it refers to the individual's reduced capacity to carry out significant tasks that are central to living a normal life, such as walking, talking, hearing, seeing, breathing, learning, working, or taking care of oneself. This concept is rooted in the Americans with Disabilities Act (ADA), which acknowledges physical or mental impairments causing such limitations. It is not solely the presence of an impairment that defines a disability, but also whether it significantly restricts essential life functions.
For example, despite having an impairment, a person with advanced hearing aids may not be considered as substantially limited in the major life activity of hearing. Additionally, mental impairments, like intellectual functioning and adaptive skills, are facets considered within these limitations. The ADA mandates reasonable accommodations to ensure accessibility and non-discrimination towards individuals faced with such limitations, enabling them to participate fully in society.