Broadcast transmits the packet to all hosts connected to the network.
Multicast transmits it to computers on the specified network group. Switches without “IGMP snooping” will forward the packet to connected hosts, so hosts which are not within the multi cast group will still see the packet but ignore. “IGMP Snooping” capable switches can detect which device belongs to which multicast group and forward the packet to only devices that belong to the intended group.