Available Definitions:
1) adv. / a. - Offhand; without previous study; extemporaneous; extempore; as, an impromptu verse.
2) n. - Something made or done offhand, at the moment, or without previous study; an extemporaneous composition, address, or remark.
3) n. - A piece composed or played at first thought; a composition in the style of an extempore piece.