Explanation: An HMO, or Health Maintenance Organization, plan does require a "gatekeeper" but also focuses on lower health care costs for patients and care that aims to prevent higher costs later on. A PPO, or Preferred Provider Organization, plan does not require that patients first contact a "gatekeeper" for medical treatment but allows patients to choose from a broad network. A POS, or Point of Service, plan offers a network (like a PPO) but allows patients to meet with a physician outside this network and request reimbursement later on. An FFS, or Feeforservice, plan is generally the most costly for patients but allows them to make their own selection of facilities and physicians.