A federal government program that provides health insurance coverage to eligible adults aged 65 or older and people with disabilities. It has four parts: Part A, which covers institutional services, including inpatient hospital services, nursing home care, initial home health visits, and hospice care; Part B, which covers physicians and other professional services, outpatient clinic or hospital services, laboratory services, rehabilitation therapy, and home health visits not covered by Part A, among other services; Part C, the Medicare Advantage program, which is managed by private companies for a flat fee per patient per month; and Part D, which began in 2006 and covers medication.