NAT is a many-to-one address translation. That is many computers on a private network, can access the internet, via 1 gateway, and 1 real IP address.

All connections outbound appear to be coming from the WAN interface of that gateway. The NAT device maintains these connections, ensuring they get to the original PC within the private network. Hence Network Address Translation.

PAT is a many-to-one port translation. Say for instance, you have a NAT gateway, and you want to open 2 ports into your LAN. you want port 80 (http) traffic to goto a web server on your lan, and you want port 25 (smtp) to goto your mailserver. Your NAT/PAT device will translate any connections made to its WAN interface on these 2 ports and route the traffic through to the respective server.

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NAT can be 1:1, many:one, or even m:n
If it is not 1:1 then on outgoing packets you may also need to change the source port number to make the packet uniquely identifiable. This can be called NAPT.


Changing a port number by itself has nothing to do with private IP addresses.
I think different people use the term PAT with different meanings at times.
I am not sure myself, and I am sure the webopedia is referring to napt, while d0t is talking about what I would think of as NAT of inbound traffic (also called port-forwarding).

RFCs 2663 and 3022 refer to NAT and NAPT. PAT is not mentioned.