Soap Operas.
Soap refers to the genres commercial origins, format emerged from radio sponsorship by detergent companies in the 1930’s
What is soap opera today? A serialised narrative, with as The Gaspodesaid no fixed resolution.
Characteristics include:
A three camera set-up, each scene is only filmed once but with three cameras, shots are edited together to form what you see on screen.
They are videoed not filmed
They tend to have a naturalistic feel, and don’t usually dramatise events with fancy camera work or lighting, mainly due to time constraints.
There are more, anything common characteristic between programs you consider a soap can be listed here. (about family life for instance,
Genre studies is not an exact science at all, the lines between genres blur and overlap often creating new genres, i.e. the docu-soap. And it’s pretty subjective. And f course there are difference between American Soaps and British soaps.
I don’t consider Casualty a soap opera, there is only one episode per week, (Soap usually run at least three times a week) and the main story is wrapped up in a single episode. In fact it’s Episodic in nature, unlike a soap in which stories continue and are serial in nature. Although of course there are serial narrative elements, showing where the line between drama and soap blur.
Only having a single episode a week, it’s filmed like a drama, it doesn’t use the three camera set-up and can afford to spend more time n lighting an camera work giving the whole episode a more ‘dramatic’ feel.
I don’t watch the Bill so I can’t comment but maybe it’s more episodic in nature. From what I have read it started very episodic and should have been classed as a Police Drama, but now it has more sop elements (serial narrative etc)
There are loads of books on the subject, just search for genre studies on Amazon.