Forum theatre was a method developed by Augusto Boal in the Latin Americas during the 70s [1]. It was also called Theatre of the Oppressed.
In this process the actors or audience members could halt a performance, often a short scene in which a character was being oppressed in some way. The audience would suggest different actions for the actors to carry out on-stage in an attempt to change the outcome of what they were seeing.
In the Nordic Larp conversation
Theatre of the Oppressed (2013) by Malik Hyltoft was played at Fastaval. A cast of 19 players of villagers and political activists use the forum theatre form together.