HMO: Health maintenance organizations (HMO) have an established provider network and only cover services by an in-network provider. The coverage map for these type of plans are no smaller than a county.
PPO: Preferred provider organizations (PPO) have an established provider network and allow the enrollees to receive medical care outside of the network. The cost sharing will be much higher for the medical care received outside of the network. Coverage map for these type of plans are also no smaller than a county.
*According to the Kaiser Family Foundation 62% of Medicare Advantage enrollees are in a HMO and 31% in a PPO.
SNP: Special Needs Plans (SNP) are HMOs that are restricted to beneficiaries who: (1) are dual eligible for Medicare and Medicaid; (2) reside in long-term care institutions or that require institutional levels of care; or (3) have certain chronic conditions.
PFFS: Private For Fee Service Plans (PFFS) determine how much it will pay doctors, hospitals, and other medical services and how much the enrollee themselves will also pay.
Most of these plans do not have an established physician network, therefore you can see any doctor or hospital who accepts Medicare and the terms and conditions of your separate Part D plan.
Group Plans: Sponsored mainly by employers and unions for retirement. The employer or union is contracted with an insurer that then provides Medicare benefits and additional retiree health benefits.