A laugh track is a separate soundtrack with the sound of audience laughter, made to be inserted into TV comedy shows and sitcoms. Laugh tracks are meant to be used as a "cue" for the viewing audience to laugh at the appropriate time during a TV show.
TV critics have often claimed that laugh tracks are used to cover up problems with the writing of a TV show, by using artificial "canned" laugh tracks to make the show seem "funnier" than it actually is.
Several TV comedy series have aired completely without laugh tracks, but in the United States these shows are few and far between. The most successful US TV comedy show to air completely without a laugh track or "live" audience laughter is The Simpsons.
The creator of the TV series M*A*S*H stated that he initially wanted the show to air entirely without a laugh track, but this idea was rejected by the CBS TV network. Eventually a compromise was reached, and the laugh track was omitted from all operating room scenes on the show. Some syndicated and international versions omitted the laugh track completely, and the DVD release gives the viewer a choice of laughing or non-laughing soundtracks.
In Britain most sitcoms are taped before live audiences to provide natural laughter. Some shows do omit laugh tracks altogether, notably The Royle Family and The Office. The League of Gentlemen was originally broadcast with a laugh track, but after the first two series this was dropped, probably at the insistence of its cast/creators.