A federal government health insurance program for people age 65 and older, certain younger people with disabilities and people with end-stage renal disease. Medicare has four parts: Part A covers hospital bills. Part B covers doctor bills. Part C, also known as Medicare Advantage, offers options run by Medicare-approved private insurance companies to get the benefits and services covered under Part A and Part B and, in some cases, prescription drug coverage (Part D). Part D helps pay for prescription drugs.