Impromptu /(?)/

Im·promp·tu

Impromptu

adv. [or] a.
  1. Offhand; without previous study; extemporaneous; extempore; as, an impromptu verse.

Impromptu

n.
  1. Something made or done offhand, at the moment, or without previous study; an extemporaneous composition, address, or remark.
  2. A piece composed or played at first thought; a composition in the style of an extempore piece. (Mus.)