The Free On-line Dictionary of Computing (30 December 2018):

Port Address Translation

    (PAT) A function provided by some routers which
   allows hosts on a LAN to communicate with the rest of a
   network (such as the Internet) without revealing their own
   private IP address.  All outbound packets have their IP
   address translated to the routers external IP address.
   Replies come back to the router which then translates them
   back into the private IP address of the original host for
   final delivery.

   Compare SOCKS.

   (1998-05-08)