From The TV IV
Single-camera programs are presented through the perspective of only one camera, using the same method as most films. Most television dramas (except soap operas) are single-camera productions. A growing number of comedies are moving to single-camera formats as well, like Scrubs, Arrested Development, and My Name is Earl.
It allows tremendous freedom, since the camera can be placed anywhere, at any angle, and move anywhere, but it can be a difficult process. To film a conversation between two characters and edit together shots of both characters' faces, the entire scene is shot from one angle, then the camera is moved, the lighting is adjusted, and the scene is repeated. The extra effort pays off, as single-camera shows are generally considered to be aesthetically superior.
See also multi-camera.