The term literally means "music drama" with music being used to increase the emotional response or to suggest characters. There is a tidy structure or formula to melodrama: a villain poses a threat, the hero escapes the threat (or rescues the heroine) and there is a happy ending. In melodrama there is constructed a world of heightened emotion, stock characters and a hero who rights the disturbance to the balance of good and evil in a moral universe.
In recent decades the term has taken on pejorative connotations.
By the end of the 19th century the term melodrama had nearly exclusively narrowed down to a specific Genre of salon entertainment: more or less rhythmically spoken words (often poetry) - not sung, sometimes more or less enacted, at least with some dramatic structure or Plot - synchronised to an accompaniment of music (usually piano). It was looked down on as a genre for authors and composers of lesser stature (probably also the reason why virtually no realisations of the genre are still remembered). This was probably also the time when the connotation of cheap overacting first became associated with the term. As a cross-over genre mixing narration and chamber music it was eclipsed nearly overnight by a single composition: Schoenberg's Pierrot Lunaire (1912), where Sprechgesang was used instead of rhythmically spoken words and which took a freer and more imaginative course regarding the plot prerogative.
The use of unsung musical accompaniments to action on stage was a precursor of the modern Film score; almost all modern films contain a musical backdrop at some point.
In most current usage, the sensationalistic plots of these original melodramas have swallowed up the other senses of the word. Melodrama as currently used is a mildly Pejorative word in literary and other sorts of criticism, meaning a drama primarily characterised by sensational plots and blatant emotional appeals to conventional sentiment, but which is typically distinguished from tragedy by often having a happy ending. When melodrama is used in the pejorative sense, it is usually because the critic feels that the sensationalism of the plot lacks Realism, or that the characters are stock heroes and villains with little room for characterization. Melodrama is ubiquitous on television: it is evident, for example, in a long series of TV movies about diseases or domestic violence, or the large number of hour-long television programs about lawyers, Police officers, or physicians.
Issues melodrama is a subspecies of melodrama in which current events or politics are given a dramatic treatment, hoping to use some recent crime or controversy as a vehicle to draw an emotional response from the viewer. The usual method is to involve lawyers, police officers, or physicians, who can then make speeches about the crime or controversy being dramatized. By this artifice, the dramatist seeks to engage the audience's recently refreshed sense of fear or moral disapproval, while simultaneously maintaining the posture that the drama so produced is timely and socially engaged.
Action melodrama is another subgenre of melodrama that is particularly prevalent in the action Hollywood film Blockbuster. An athletic action hero is pitted against an evil villain, and through a bevy of fights, car chases, love scenes and splatter, the hero overcomes the villain and restores the balance of good in the universe. This subgenre often includes a heroine who fights and loves with the hero. Sylvester Stallone and Arnold Schwarzenegger are examples of the stars of these action melodramatic flicks.
Informal use / Slang Casual use of the word as an adjective translates to exaggerated emotions or ways in expressing oneself. For example: "Don't be so melodramatic!" which can be said to a 'Drama Queen' (someone who often overeacts to situations).