[X4U] What is NAT and what does it mean to me?

[B. Kuestner]

Network address translation.

Your router has a public address in the internet. But behind the  
router each machine (even if it's just one) is in a local network  
with its own private address range.

Any data in an IP-network goes from IP address to IP address. The  
webserver will send data to the router via its public address. Then  
the router must translate the address for the requested data so they  
reach your computer.

<http://en.wikipedia.org/wiki/Network_address_translation>

Björn