A federal program that pays for certain health care expenses for people aged 65 or older. Enrolled individuals must pay deductibles and co-payments, but much of their medical costs are covered by the program. Medicare is less comprehensive than some other health care programs, but it is an important source of post-retirement health care. Medicare is divided into four parts. Part A covers hospital bills, Part B covers doctor bills, Part C provides the option to choose from a package of health care plans, and Part D offersprescription drug coverage.