According to the Social Security Administration:
Disability: The inability to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairments which can be expected to result in deal or which has lasted or can be expected to last for a continuous period of not less than 12 months.
Impairment: Functional restrictions (cognitive/physical) that result from anatomical, physiological, or a psychological abnormalities which are demonstrable by medically acceptable clinical and laboratory diagnostic techniques.
According to Bradely et al, Disability and Rehabilitation, 1993:
Disability: Any restriction or lack (resulting from an impairment) of the ability to perform an activity in the manner or within the ranges considered normal for a human being.
Impairment: Any loss of abnormality of psychological, physiological, or anatomical structure or function.
Handicap: A disadvantage fo a given individual resulting from an impairment or a disability, that limits or prevents the fulfillment of a role that is normal (depending on age, sex and social and cultural factors) for that individual.
An impairment stands alone, without a disability or handicap present. A disability dictates that an impairment must be present. A handicap dictates that either an impairment or disability must be present.
Permanent total disability is when a claimant meets a listing of injuries which presume total disability, and benefits are paid through the lifespan of the claimant.
A temporary total disability is presumption of short-term inability to work. Benefits are of weekly income replacement when the worker is expected to recover and return to work.
Permanent partial disability is when a claimant loses total use of a member of the body, such as an eye, foot or finger.
Temporary partial disability is when an injured worker is partially incapacitated during the course of the work day on which the injury occurs, and is subsequently able to work without permanent impairment, part-time or light-duty status until full recovery.
Social Security Disability Insurance (SSDI) provides benefits to pay lost earnings to disabled workers whose disability is expected to last more than a year. Supplemental Security Income (SSI) provides payments to disabled children up to age 18 and those over age 65. Workers Compensation is a state based Social Insurance benefit.