Port forwarding is the redirecting of computer signals to follow specific electronic paths into your machine.
We call these little cars “transfer packets”.
When this happens, it is called “packet filtering” or “packet sniping.”

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What Ports Do Computer Packets Like to Use?
Every software in your machine is usually programmed to send its packets through a specific port.
These port choices are often established as programming standards in the computer industry.
How Can I Learn How to Program My Router’s Port Forwarding Commands?
Towards these ends, there is a splendid resource by the folks at www.portforward.com.