A MAC broadcast works in much the same way as an IP broadcast. When sending an IP broadcast, one must also send a MAC broadcast. With an understanding of the TCP/IP Reference Model and how ethernet works this makes sense. When a host sends a packet out, it adds to it in the order of Application, Transport, Internet, and finally Network Interface.
When this packet is recieved it is read in reverse. So the IP broadcast which is asking all hosts within a given IP range to respond is not the first thing a host processes. The first thing a host sees as the packet comes its way is the MAC address. If this MAC address is not relevant to the host, it will not read the rest of the packet. So an IP broadcast would not get to all hosts. That is unless the MAC address was also a broadcast address and all hosts responded to it.
This is the MAC broadcast address, and like the IP broadcast it is a binary sequence of all ones. This is a 48-bit address, so referring to the MAC broadcast address as a string of 48 ones is a little ungainly. Like other MAC addresses, it is converted into hexadecimal; the MAC broadcast address is therefore FF-FF-FF-FF-FF-FF.
Note: As with IP broadcasts, routers terminate MAC broadcasts, so that WANs aren't bogged down by them.