From The TV IV
Multi-camera programs are filmed by two or more cameras simultaneously. This allows multiple camera angles to capture the same event, either edited together on the fly, or in post-production. Most programs that are filmed live are shot with mutiple cameras, including sitcoms, newscasts, game shows and special events, such as sporting contests or award shows. Many soap operas are also multi-camera productions, for budgetary reasons.
The format is efficient (and cheap), since several shots can be obtained from actors in one take, but it is also limiting. Because it's important not to film one of the other cameras, certain angles can not be shown, and it's difficult to use moving or hand-held cameras to capture some action.
See also single-camera programs.