EPO stands for Exclusive Provider Organization. EPOs are similar to HMOs — you have access to a specific network of care providers and there is no out-of-network coverage, except in the case of emergencies. However, you can see specialists without a primary care physician's referral.
Like HMOs, EPOs often have lower premiums than PPOs and your annual spend may be less than in a PPO, assuming you avoid out-of-network care.
If you like the idea of a plan with a specific network of providers, but want a little more flexibility seeing specialists than an HMO but a lower cost alternative to a PPO, EPOs can be a great option. If this type of network constraint does not include your your existing doctors or facility needs, a PPO is likely to be a better option for you.