Preferred Provider Organization (PPO)
A. Plan that requires you to work with a primary care physician who will direct your care.  Requires you to use in-network providers.
B. Plan that combines elements of PPO and HMO.  You can use a primary care physician or direct your own care.
C. Plan allows you to see any doctor at anytime.  Usually has a co-payment and is cheaper if you use in-network providers.