Hello,
a broadcast is a message sent to all machines in a VLAN or IP subnet.
The reason to do this is f.e. to find a specific machine which you do not know yet. An example for this would be an ARP request: "Who has the IP 10.1.1.1?" to find the MAC address of 10.1.1.1, which is not known by the sender of the ARP request.
There are plenty of other examples like this.
Hope this helps!
Regards, Martin
