There are many different types of health insurance available in the United States, and each one has its own set of rules and regulations. AOK is a type of private health insurance, which means that it is not provided by the government. Private health insurance plans are typically offered by employers, but they can also be purchased directly from an insurer. AOK is a PPO (Preferred Provider Organization) plan, which means that you can see any doctor or hospital that accepts AOK insurance, but you will pay less if you use a provider that is in the AOK network.