Short answer: These describe how a plan manages access to providers. An HMO requires a primary care physician and referrals and generally covers only in-network care; a PPO is the most flexible (no referrals, some out-of-network coverage); an EPO covers only in-network care but skips referrals; and a POS plan blends HMO and PPO features.
Health plans are often labeled by how they manage your access to doctors and hospitals. The trade-off is almost always flexibility versus cost: more freedom to choose providers usually means a higher premium.
HMO (Health Maintenance Organization): you pick a primary care physician (PCP), need referrals to see specialists, and the plan generally covers only in-network care (except emergencies). Lower premiums, less flexibility.
PPO (Preferred Provider Organization): no PCP or referrals required, and the plan covers out-of-network care at a lower benefit level. The most flexible and usually the most expensive.
EPO (Exclusive Provider Organization): like a PPO in that you don’t need referrals, but like an HMO in that there’s no out-of-network coverage (except emergencies). A middle option.
POS (Point of Service): a hybrid. You choose a PCP and need referrals (like an HMO) but have some out-of-network coverage (like a PPO).
In every plan type, true emergency care is covered as in-network under federal law, no matter where you receive it.