Im*promp"tu (?), adv. or a. [F. impromptu, fr. L. in promptu in readiness, at hand; in in + promptus visibility, readiness, from promptus visible, ready. See Prompt.] Offhand; without previous study; extemporaneous; extempore; as, an impromptu verse.

Im*promp"tu, n. 1. Something made or done offhand, at the moment, or without previous study; an extemporaneous composition, address, or remark.

2. (Mus.) A piece composed or played at first thought; a composition in the style of an extempore piece.

• Improvised; without prior preparation; extemporaneous; unplanned.
       The party began with an impromptu rendition of 'Happy Birthday'.
  
• A category in high school speech competitions, using a randomly-drawn topic to compose a brief, humorous speech.
  
• (music) a short musical composition for an informal occasion often with the character of improvisation and usually to be played solo.