A soap opera, sometimes called "soap" for short, is an ongoing, episodic work of dramatic fiction presented in serial format on television or radio. Programs described as soap operas have existed as an entertainment long enough for audiences to recognize them simply by the term soap. The name "soap opera" stems from the original dramatic serials broadcast on radio that had soap manufacturers such as Procter and Gamble, Colgate-Palmolive, and Lever Brothers as sponsors and producers. These early radio serials were broadcast in weekday daytime slots when mostly housewives would be available to listen; thus the shows were aimed at and consumed by a predominantly female audience.

The term soap opera has at times been generally applied to any romantic serial, but it is also used to describe the more naturalistic, unglamorous UK primetime drama serials such as Coronation Street. What differentiates a soap from other television drama programs is the open-ended nature of the narrative with stories spanning several episodes. The defining feature that makes a program a soap opera, according to Albert Moran, is "that form of television that works with a continuous open narrative. Each episode ends with a promise that the storyline is to be continued in another episode".

Soap opera stories run concurrently, intersect and lead into further developments. An individual episode of a soap opera will generally switch between several different concurrent story threads that may at times interconnect and affect one another or may run entirely independent of each other. Each episode may feature some of the show's current storylines but not always all of them. There is some rotation of both storylines and actors so any given storyline or actor will appear in some but usually not all of a week's worth of episodes. Soap operas rarely "wrap things up" storywise and generally avoid bringing all the current storylines to a conclusion at the same time. When one storyline ends there are always several other story threads at differing stages of development. Soap opera episodes typically end on some sort of cliffhanger.

In 1976, Time magazine described American daytime television as "TV's richest market," noting the loyalty of the soap opera fan base and the expansion of several half-hour series to a full hour in order to maximize ad revenues. The article explained that at that time, many prime time series lost money, while daytime serials earned profits several times more than their production costs. The issue's cover notably featured its first daytime soap stars, Bill Hayes and Susan Seaforth Hayes of Days of our Lives, a couple whose onscreen and real-life romance was widely covered by both the soap opera magazines and the mainstream press. Though American soap opera ratings have declined over the last 30 years, the Latin American version of soap opera — called a telenovela — remains the most-watched genre of television program in the world, with at least two billion viewers worldwide.

Evening soap operas sometimes differ from this general format and are more likely to feature the entire cast in each episode and to represent all current storylines in each episode. Additionally, evening soap operas and other serials that run for only part of the year tend to bring things to a dramatic end-of-season cliffhanger.