The Code of Federal Regulations, Volume 20,
Section 404.1505, sets out Social Security's basic
definition of disability as "the inability to do any
substantial gainful activity by reason of any medically
determinable physical or mental impairment which
can be expected to result in death or which has lasted
or can be expected to last for a continuous period of
not less than 12 months."
This definition of disability is unique to the Social
Security Act, and is the same for all disability benefit
programs administered by the Social Security
Administration. You must have physical or mental
problems (or a combination of both) severe enough to
keep you from working in any regular paying job
("substantial gainful activity") for at least 12 months.
Disability due to drug and alcohol addiction is not
covered, but certain physical or mental conditions as a
result of a prior addiction may be covered.
Importantly, the test is not whether you would be offered a job, or whether an employer would hire you, but whether you have the physical and mental ability to perform a given job if you had it.
For those over 50 years of age, new regulations allow a more realistic consideration of your age, education, and prior work experience when considering whether you meet this test. In other words, if you are age 50 or over, you may still possibly be considered disabled even if there is some other work you are still capable of doing.