An act is a major division of a theatre work, including a play, film, opera, ballet, or musical theatre, consisting of one or more scenes.^[1][2] The term can either refer to a conscious division placed within a work by a playwright (usually itself made up of multiple scenes)^[3] or a unit of analysis for dividing a dramatic work into sequences. The word act can also be used for major sections of other entertainment, such as variety shows, television programs, music hall performances, cabaret, and literature.

An act is a part of a play defined by elements such as rising action, climax, and resolution. A scene normally represents actions happening in one place at one time and is marked off from the next scene by a curtain, a blackout, or a brief emptying of the stage.^[1]

The elements that create the plot of a play and divide it into acts include the exposition, which sets up the rest of the story by giving basic information. Another element is the inciting incident, which starts all the action that will follow. Going along with the inciting incident, the major dramatic question is formed, which holds the rest of the play. The majority of the play is made up of complications, which change the action. These complications lead to the crisis, which is the final plot point. At this point, the major dramatic question is usually answered. Finally, the play culminates with a resolution, or the dénouement, where everything comes together and the situation has been resolved.^[4] These elements of the plot are the main things used to divide a play into acts and sometimes scenes. In some scenarios, the play may not end with a resolved situation; it may leave the audience on a peak and have a sequel to it, otherwise known as a cliffhanger.

Though there is no limit to the number of acts in a dramatic work, some may have been derived from different interpretations of Aristotle's Poetics, in which he stresses the primacy of plot over character and "an orderly arrangement of parts",^[5] and others may have been derived from Freytag's Pyramid.^[6]

Roman theatre was the first to divide plays into a number of acts separated by intervals. Acts may be further divided into scenes.^[7] In classical theater, each regrouping between the entrances and exits of actors is a scene, while later use describes a change of setting.^{[citation needed]}

Modern plays often have only one level of structure, which can be referred to as either scenes or acts at the whim of the writer, and some writers dispense with firm divisions entirely.^{[citation needed]} Successive scenes are normally separated from each other in either time or place, but the division between acts has more to do with the overall dramatic structure of the piece. The end of an act often coincides with one or more characters making an important decision or having an important decision to make, a decision that has a profound impact on the story being told.^{[citation needed]}

Contemporary theatre, in line with screenwriting and novel forms, tends towards a three-act structure. Many operettas and most musicals are divided into just two acts, so, in practice, the intermission is seen as dividing them, and the word act comes to be used for the two-halves of a show whether or not the script divides it into acts.

As part of a television program, each individual act can be separated by commercials.

In film, a number of scenes grouped together create a story. The three-act structure is commonly referred to in film adaptations of theatrical plays.

• Acting