To send data to a specific list of recipients. Cable television is an example of narrowcasting since the cable TV signals are sent only to homes that have subscribed to the cable service. In contrast, network TV uses a broadcast model in which the signals are transmitted everywhere and anyone with an antenna can receive them.
The Internet uses both a broadcast and a narrowcast model. Most Web sites use a broadcast model since anyone with Internet access can view the sites. However, sites that require you to log-in before viewing content are based more on the narrowcast model. The various push technologies are another form for narrowcasting. Perhaps the best example of narrowcasting are e-mail lists where messages are sent only to individuals who subscribe to the list.
The terms multicast and narrowcast are often used interchangeably, although narrowcast usually refers to the business model whereas multicast refers to the actual technology used to transmit the data.