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From Wiki- might help define "sitcom"--

As opposed to standup comedy, or the telling of jokes, the situation comedy has a storyline plot and is more or less comedic drama. The essence of the current, modern situation comedy on television is that the characters remain in the same situation from episode to episode. The situation is usually that of a family, workplace, or a group of friends. The term was adopted to distinguish the sitcom from other comedy formats: sketch comedy, which generally featured new characters and situations each outing, or the humorous monologue or dialogue, which did not feature characters. Often these other formats were presented within a variety format mixed with musical performances, as in vaudeville. The emerging mass medium of radio allowed audiences to return to programs over and over, which allowed programs to return to the same characters and situations each episode and expect audiences to be familiar with them. Thus, while the humor in sitcoms varies, it is usually character-driven, which may result in running gags during the series.
Due to the need to retain the same situation over many episodes, in many sitcoms characters remained largely static. Events of individual episodes typically resolve themselves by the end, and are rarely mentioned in subsequent episodes. This episodic nature is mirrored in many dramas as well, but there are also many sitcoms that feature story arcs across many episodes, where the characters and situations slowly change over the course of their run.