Multicast

is a technology that allows many people to receive an audio or video stream across the Internet from a single data feed. It is much like a "party line" (remember those?) in which multiple households shared a single telephone line and everyone could listen in on the same telephone call just by picking up the receiver. Multicast makes it possible to send an audio or video stream to a large number of people without using a large amount of network capacity.

Related term: Unicast