Permanent disability is the legal term for the long-term loss of function caused by a work injury, after the worker has reached maximum medical improvement. It's expressed as a percentage of either the affected body part or, in some cases, the body as a whole.
The disability rating drives the dollar value of the permanent portion of a workers' compensation claim. Higher ratings mean more weeks of benefits at the worker's compensation rate.
Both Missouri and Illinois use specific schedules for body-part disabilities (so many weeks of benefits for total loss of a hand, foot, eye, etc.) and 'whole body' ratings for injuries that don't fit the schedule.