What are disabilities?
The term "disability" covers a wide range of physical and cognitive conditions, regardless of cause (accident, genetic condition, disease) -- for example, learning disabilities, traumatic brain injury, multiple sclerosis, cerebral palsy, spinal cord injury, drug abuse and alcoholism, polio, HIV/AIDS, and Alzheimer's, to name only a few.
Disabilities might be permanent or temporary. Something like diabetes might not be considered a disability in itself, but may cause other conditions that are considered disabilities. Individuals sharing the exact same diagnosis may have differing backgrounds, support networks, education, and employment histories -- all of which impact self perception and the resources available to each person.
Something is generally considered a disability when it impacts one or more major life activities (also called "activities of daily living"). The Americans with Disabilities Act (ADA), which many people turn to as a common reference point, covers an estimated 49 million Americans -- including about 2.6 million New Yorkers -- who have physical or mental impairments that substantially limit such activities as walking, talking, hearing, seeing, working, and caring for oneself.
Under the ADA, people might not actually have a disability at the moment, but if other people perceive them as having a disability, they are afforded the same protections as if they did. An example of this might be a cancer survivor -- someone who is in remission, and therefore does not currently have a disability, but who is still protected against discrimination by people who might perceive them as less capable of handling a promotion, for instance.