unpremeditated; impromptu

To improvise; to extemporize.

plural of improvising

a form of theatre in which the actors perform spontaneously, without a script

A form of improvisational theatre performed with little predetermination of subject matter and structure, but with interaction with the audience. / An instance of such theatre.

plural of improvisational comedy

An unconventional or amateur explosive weapon made from nonmilitary components, especially one used by guerillas, commandos or terrorists.

plural of improvised explosive device