Extemporization
Part of speech: noun
Definition: The act of extemporizing; the act of doing anything extempore.
Improvisation
Part of speech: noun
Definition: The act or art of composing and rendering music, poetry, and the like, extemporaneously; as, improvisation on the organ.That which is improvised; an impromptu.Musical technique, characteristic of blues music.
Example sentence: I had two starts, really. The first was going to the Italia Conti stage school, aged 15. I'd gone to sing, but one day I found myself doing an improvisation and thought, 'Oh God, I quite like this acting thing.' The second start was meeting Mike Leigh when I was 22. He showed me I could play people that weren't like me.