Multicasting is communications from one sender to a defined group of receivers in a network. Multicasting is the opposite of unicasting, which is communication between one sender and one receiver. In radiocommunications, multicasting is more commonly reffered to as point-multipoint communications (P-MP).
Multicasting differs from broadcasting in the fact that, with broadcast, the network simply spreads the information to all the nodes within the network. With multicast,the information is sent only to defined nodes, i.e. members of a group. Data is transmitted in an optimal manner with minimal duplication.
Multicast transmission is an important component of many current and future application on the Internet, such as videoconference, distance learning and audio and video distribution.