Each of the four parts of the Medicare public health insurance plan covers specific health-related expenses. Part C is the third of the four parts and combines parts of the coverage offered in Part A and Part B. Part C, also commonly called Medicare Advantage, is a combination of public insurance and private insurance. This form of insurance is provided by private insurance companies and includes both Part A coverage and Part B coverage as provided by Social Security, along with coverage that is not offered by Medicare. This hybrid of public and private insurance helps citizens who qualify for Medicare receive all of the coverage that they need in a simplified plan.