Noun
English Wikipedia has an article on:improvisational theatreWikipedia
improvisational theatre (uncountable)
a form of theatre in which the actors perform spontaneously, without a script
Improvisational theatre, often called improv or impro, is a form of theater where most or all of what is performed is created at the moment it is performed. Source: Internet
Improvisational theatre exists in performance as a range of styles of improvisational comedy as well as some non-comedic theatrical performances. Source: Internet