Medicare Parts A & B
Medicare Part A generally covers hospice, hospital, skilled nursing, and home health care services. Medicare Part B covers preventative services as well as supplies and services medically necessary to treat a disease or condition.
Medicare Supplement (Medigap) plans provide coverage that Original Medicare doesn't cover in full. They are regulated by state and federal government. Identified in most states by letters, all policies provide the same basic benefits, however, some provide additional benefits.
Medicare Part D
This is your drug plan. Each plan has its own list of covered drugs (formulary). Many plans have different "tiers" on their formularies. Drugs in each tier have a different cost. Be careful to choose your plan based on the drugs you are taking.
This is a health plan offered by a private company that replaces your Original Medicare to provide you with your Part A and Part B benefits. Most include Part D coverage as well and some plans may also provide vision and dental.