Medicare part D is an optional coverage that covers prescription drug. This means that it is used to help pay for prescribed medications for out-patients. This type of coverage is provided by private companies that have been approved by Medicare. To become an eligible candidate for Medicare Part D, you only need to have a Medicare Part A coverage and Medicare Part B. You can get the coverage as an independent coverage or as part of a Medicare Advantage plan. It is also important to note that Medicare Part D plan is also referred to as the Medicare prescription plan.