Composed, performed, or uttered on the spur of the moment, or without previous study; unpremeditated; off-hand; ad-lib; extempore; extemporary; as, an extemporaneous address or production.

with little or no preparation or forethought; "his ad-lib comments showed poor judgment"; "an extemporaneous piano recital"; "an extemporary lecture"; "an extempore skit"; "an impromptu speech"; "offhand excuses"; "trying to sound offhanded and reassuring"; "an off-the-cuff toast"; "a few unrehearsed comments"

An impromptu or spontaneous presentation.