“Regarded as” means that the person either:

• Has an impairment that does not substantially limit a major life activity;
• Has an impairment that substantially limits a major life activity only as a result of the attitudes of others toward them; or
• Does not have any impairment, but is treated by an entity as having an impairment.

For additional information, take a look at the following resources:

FAQ: Can you give me an example of someone who is “regarded as” having a disability? [2] 

FAQ: What are major life activities? [3]

FAQ: Who is protected from employment discrimination? [4]

FAQ: What is the definition of disability under the ADA? [5]