Gestus is a neologism, a word Brecht coined, although he used it in different ways at different times in his writings. In connection with the actor it has two primary meanings
Gestus as Social Physicality
Brecht encourages actors to enter the stage conscious that their bodies are also significant. A male roofer’s body should look different from a female carpenter’s, for example, but both would tell the audience that they are engaged in manual labour. An office worker would thus look different from a manager, a teacher from a head teacher. In each case, the body signifies a relationship between individual and society. This kind of physicalised Gestus helps the audience to contextualise the figure on stage and to suggest that what the figures are doing and how they behave owes something to their position in society. However, it should be noted that this relationship is not in some way reductive. The roofer could present the audience with a body wrecked by the long hours required to pay bills and provide for dependents, but it could also display strength and confidence, the pride of an artisan in his work. It is the job of the director and the actors to understand the contradictions of the socialized body and to bring them out as clearly as possible in performance.
Haltung is a term closely bound to Gestus, and you should read that page to understand the relationship. However, a figure may have a repertoire of gestures that are not an example of Haltung. That is, a figure’s social position may produce a typical set of gestures. In the documentation for Closer, for example, Dan has an air of superiority, born of his middle-class status. The gestures associated with this aren’t Haltungen because they aren’t specific, physicalised attitudes to specific people, ideas or actions. Instead, they are more general gestic features of the figure’s place in society. So, a haughty look or a lack of interest in what another figure is saying are expressions of the figure’s overall Gestus. These features are not, however, characteristics, as these tend to be understood as unchangeable, psychological facets of a character. Gestus is a social and not a natural category, and is thus subject to change as society changes. And it should be noted that Dan is one example of a middle-class figure, and others may suggest very different kinds of typical gestures. A middle-class liberal, for example, may exhibit an exaggerated sensitivity to people of other genders or races; a middle-class heir may display a sense of entitlement or humility.
Gestus and Action
If the body is no longer ‘innocent’, in that it’s implicated in the workings of society, then actions, too, may have a Gestus. Consider the Bible story of the betrayal of Jesus. Judas identifies Jesus to the Romans by kissing his cheek. Brecht would say that the kiss had to have the Gestus of betrayal and/or self-enrichment included so that an audience could understand the contradictory meaning of the action: a kiss leads to crucifixion for Jesus and payment for Judas.
This notion of Gestus helps the actor perform two things as a process. The actor playing Judas would perhaps kiss Jesus while focusing on the watching Romans, or kiss with a look of regret or a look to his thirty pieces of silver. There are many ways of performing this particular Gestus.
Brecht believed that all actions had a Gestus that pointed to processes and meanings that underlay them. The actor’s job is thus to discover this Gestus as a way of offering the audience Verfremdung, making a familiar action strange and pointing to what may have informed it.