There are two main parts of EPS: LTE (Long Term Evolution) and SAE (System Architecture Evolution).
Actually those two parts have also different names and LTE is known as E-UTRAN and SAE is known as EPC (Evolved Packet Core).
MME - Mobility Management Entity
S-GW - Serving Gateway
HSS - Home Subscriber Server
PCRF - Policy Control and Charging Rules Function
PDN-GW - Packet Data Networks Gateway