improvisation, especially as part of a comedy routine or as a theatrical technique;
e.g. The group put on a show of improv that made the audience roar with laughter.
(adjective)
relating to or consisting of the action of presenting or performing something with minimal preparation or rehearsal, especially describing a comedy routine whose content is largely spontaneous;
e.g. He is great at improv theatre, and he can act out any scene with barely any preparation.