What is hostname?

In plain language

Every device on a network has an address; most also have a name. Type the name into a browser and, if your network resolves it, you land on the device. Names are usually short and derived from the model plus something unique, so several identical units do not collide.

Why it matters in your setup

Names are stable in a way addresses are not, which makes them the practical way in for day-to-day use. And in a rack with more than one identical box, the serial-derived suffix is the only thing telling you which one you are about to reconfigure.

Whether a name resolves depends on the network. Some routers register DHCP names automatically, some do not. As with mDNS, the IP address stays the fallback.

What the DR HDMI 8K does with it

The DR HDMI 8K's hostname is DR8K-XX, where XX is the last two digits of the unit's serial number, reachable at http://DR8K-XX/. It is shown on the OLED info page and in the header of every web interface page, alongside the mDNS address and the IP.