In acting, units of action, otherwise known as bits (or beats), are sections that a play's action can be divided into for the purposes of dramatic exploration in rehearsal.
The concept was propounded by the Russian actor, director and educator Konstantin Stanislavsky, who initially liked to use the term (Russian: кусок; IPA: [kʊˈsok]), an ordinary Russian word that can be translated as "bit" – as in a bit, or slice, of bread or meat. This was the term Stanislavsky preferred in the original drafts of his books. Stanislavsky also referred to these bits of action as episodes (longer sections), events, and facts (shorter segments), and these were the terms that he preferred to use towards the end of his life.
The term unit was introduced in the standard early translations of Stanislavsky's writings. Use of the word "beat" in the place of "bit" has become mainstream in American method acting. This historic mistranslation may have helped spawn the common metaphor of the dramatic script as a musical score (Stanislavsky himself used the same metaphor to refer to detailed production plans, and elsewhere it was also taken up by others, including the innovative Polish director Jerzy Grotowski as a score of physical actions).
Stanislavsky conceived the segmentation of script as a preparatory tool for actors working on a play. Although he used the Russian word for "bit" (kusok) in the drafts he originally made for his planned books, he later preferred to speak in terms of "episode" (epizod in Russian), "event" (sobytie), and "fact" (fakt). These were the terms that Stanislavsky chose to use while teaching his system of acting to students at the Opera-Dramatic Studio in Moscow in the final years of his life, when he was concerned about the risk of losing sight of the play as a whole after breaking the action down into small bits. By this time, he was consistently distinguishing between more extended "episodes" (large bits or "events") and shorter "facts" (medium or small bits or "events"), using the Russian terms he had already employed in his notes and drafts earlier in his career. In Stanislavsky's conception, division into "episodes" can reveal the basic building-blocks of action, while subdivision into "facts" can help uncover the changes that occur from one moment to the next. Such divisions can be used to help players explore their characters and discover their actions through improvisation work during the early stages of rehearsal.