A type of health insurance plan that provides Medicare benefits through a private-sector health insurer. Also known as Medicare Part C. Plans contract with the federal government and are required to offer at least the same benefits as original Medicare, but may follow different rules and may offer additional benefits. Unlike original Medicare, enrollees may not be covered at any health care provider that accepts Medicare, and may be required to pay higher costs if they choose an out-of-network provider or one outside of the plan's service area.