In multicast messaging, one host sends a message to a limited group of other hosts. Multicast packets are regenerated at each router hop in such a way that unicasts of the message to multiple hosts on the same subnet are avoided.
In IPv4, multicast is facilitated by Internet Group Management Protocol (IGMP). For IPv4, alternatives to multicast are unicast and broadcast.
In IPv6, alternatives to multicast are unicast and anycast.