28 CFR 32.23 - Definitions.
Gainful work means full-or part-time activity that actually is compensated or commonly is compensated.
(1) Will progressively deteriorate or remain constant, over his expected lifetime; or
(2) Otherwise has reached maximum medical improvement.
Product of an injury - Permanent and total disability is produced by a catastrophic injury suffered as a direct and proximate result of a personal injury if the disability is a direct result of the personal injury.
Residual functional capacity means that which an individual still is capable of doing, as shown by medical (and, as appropriate, vocational) assessment, despite a disability.
Totally disabled - An individual is totally disabled only if there is a degree of medical certainty (given the current state of medicine in the United States) that his residual functional capacity is such that he cannot perform any gainful work.