In radiocommunications, broadcasting is the transmission of information that is intended for the general public. This service includes both sound transmissions (radio) as well as video transmissions (television). For the transmission, high antenna masts and high power transmitters are used to reach as many listeners or viewers as possible.
In a network, broadcast is the simultaneous transmission of information to all nodes and terminals of a network. This is used in both fixed networks and wireless networks. E.g. in a celluar network like GSM, each base station broadcasts information such as his identity, so every mobile in the vicinity will know that it is possible to connect to the network at that particular place.
Multicasting is a type of broadcasting in which the information is only directed to users who request to see the infomration. Therefore the information only has to be transmitted in those parts of the network where users have requested it.