Meaning of impromptu

im•promp•tu

1. made or done without previous preparation: an impromptu address to the unexpected crowds.
2. suddenly or hastily prepared, made, etc.: an impromptu dinner.
3. improvised; having the character of an improvisation.

1. without preparation: verses written impromptu.

1. something impromptu; an impromptu speech, musical composition, performance, etc.
2. a character piece for piano common in the 19th century and having, despite its title, a clear-cut form.