Port forwarding
A firewall rule directing inbound traffic on a given port to a specific internal device.
It is how an internal service is made reachable from the internet, and it is one of the most common causes of compromise in smaller networks. Remote desktop forwarded straight to a server is scanned and attacked within hours.
When inbound access is genuinely required, a VPN or a published application gateway with authentication in front is the better pattern. Forwarding management protocols directly is very rarely justified.
Where this comes up
Port forwarding sits inside our networks and infrastructure work. If you are trying to work out what this means for your own environment rather than in the abstract, that is the page worth reading next, and a short call will get you a straight answer faster than either.