Multicast in simple words means Message sent to multiple peoples.
Broadcast means I leave the message and whoever can get the message.
Originally Posted by multicast
A multicast message is one that is transmitted to selected multiple recipients who have joined the appropriate multicast group. The sender has to generate only a single data stream. A multicast-enabled router will forward a multicast to a particular network only if there are multicast receivers on that network. Other stations filter out multicast packets at the hardware level (eg, Ethernet or Token Ring).