Packet Data Network (PDN) SAE Gateway or PGW. So PGW is PDN SAE Gateway.
PGW is responsible to act as an anchor of mobility between 3GPP and non-3GPP technologies. PGW provides connectivity from the UE to external packet data networks by being the point of entry/exit of traffic for the UE (User Equipment/mobile phone). A UE may have simultaneous connectivity with more than one PGW for accessing multiple PDNs. The PGW manages policy enforcement, packet filtration for users, charging support and lawful Interception. Non-3GPP technologies are listed below :- WiMAX, CDMA 1X and EvDO. PGW is shown in diagram below: