The short explanation
A single device can run several network services at once. The port number keeps them apart. Written together they look like 192.168.1.100:2201 — that address, that service.
Web interfaces use port 80 by default, which is why you never type it. Control services pick their own number, and 2201 is a common choice in AV.
Where you run into it
A control system has to be pointed at the right port or the connection simply fails, with no useful error. And if a port collides with something else on your network, changing it is the fix — as long as you change it on both sides.
How the DR HDMI 8K handles it
The DR HDMI 8K listens for IP and Telnet commands on port 2201 by default, and the port can be changed in the CONFIG section. A reboot or power cycle is needed before the new port takes effect — worth knowing before concluding the change did not work.
Want to test your own HDMI chain?
The DR HDMI 8K is sold through the HDFury.eu web shop.