A soap opera or daytime serial is an ongoing, episodic work of fiction, usually broadcast on television or radio. What differentiates a soap from other television drama programs is their open-ended nature. Plots run concurrently, and lead into further developments: there is rarely a need to "wrap things up", although soaps that run in series for only part of the year tend to bring things to a dramatic cliffhanger. The soap opera form first developed on broadcast radio in the 1920s, and expanded into television starting in the 1940s.
The USA soap opera Port Charles has begun the practice of running 13-week "arcs", in which the main events of the arc are played out and wrapped up over the 13 weeks, although some storylines do continue over more than one arc.
Most soaps follow the lives of a group of characters who live or work in a particular place.
The term "soap opera" originated from the fact that when these serial dramas were aired on daytime radio, the commercials aired during the shows were largely aimed at housewives (this was during the first half of the 20th century, when married women were expected to stay home and raise the children). Many of the products sold during these commercials were laundry and cleaning items. This specific type of radio drama came to be associated with these particular commercials, and this gave rise to the term "soap opera"—a melodramatic story that aired commercials for soap products.
A few soap opera spoofs have been made. Two of the most famous U.S. spoofs were Mary Hartman, Mary Hartman and Soap. On British television, comedian Victoria Wood a long-running spoof soap entitled Acorn Antiques features on her sketch show (loosely based on ITV's Crossroads). In the United States, Carol Burnett frequently ran a soap opera spoof on her show, called As the Stomach Turns.
The soap opera's distinctive open plot structure and complex continuity was eventually adopted in major American prime time television programs. The first significant one was Hill Street Blues produced by Steven Bochco which featured many elements borrowed by soap operas such as an ensemble cast, multi-episode storylines and extensive character development over the course of the series. The success of this series soon gave rise to a variety of other serious drama and science fiction series which took much the same elements to structure their own storylines.
The BBC continues to broadcast one of the earlier radio "soap opera" programmes in Britain, the ever popular "Archers", on Radio 4. It has been running since 1951 nationally, making it almost certainly the longest running radio soap in the world. It continues to attract over five million listeners, or roughly 25% of the radio listening population of the UK at that time of the evening.