MMI means "Maximum Medical Improvement" and is used to determine when benefits should stop being paid to the injured employee. IR means "Impairment Rating," TPD means "Temporary Partial Disability," TTD means "Temporary Total Disability," and PTD means "Permanent Total Disability." All of these categories are used to determine an injured worker's benefits. When a worker reaches MMI, their workers' compensation benefits stop. However, the doctor assesses an impairment rating, which determines the amount of benefits they may continue to receive.