Broadcast MAC address
A broadcast Ethernet frame will have the broadcast MAC address in the destination address field of the Ethernet header. The broadcast MAC address is FF:FF:FF:FF:FF:FF. A frame with this destination address will be sent to all hosts within a particular network segment/broadcast domain.
During encapsulation, an IP packet with a broadcast IP address in the destination IP address field will be further encapsulated into an Ethernet frame. The device looks at the destination IP address, and determines that it is a broadcast address. Thus the destination MAC address used in such a frame is the broadcast MAC address.