Firewall/Gateway
The name "firewall" derives from the term for a barrier that
prevents fires from spreading. A computer "firewall" is a barrier
between your computer and the outside world. Just like a fire is most likely
to spread through open doors in a building, your computer is most vulnerable
at its ports (the doors). Without ports you could not go on the Internet
or let Internet traffic enter your computer.
Gateways are points of entrance to and exit from a communications network.
Viewed as a physical entity, a gateway is that node that translates between
two otherwise incompatible networks or network segments.