Medicare Advantage, also called Medicare Part C, combines the benefits of Original Medicare (Part A and Part B) into a single plan with additional coverage, like dental, vision, hearing, and more.
Medicare Supplement, or Medigap insurance, bridges the coverage gap left by Original Medicare (Part A and Part B) and covers costs like deductibles, copayments, and coinsurance.
Medicare Part D Prescription Drug Plans (PDP) work in tandem with Original Medicare (Part A and Part B) and Medicare Advantage plans to provide prescription drug coverage. 
Dental and vision plans are additional ancillary products beneficiaries can purchase (as standalone or part of Medicare Advantage) since they are not included in Original Medicare (Part A and Part B) coverage.
