a short musical passage that seems to have been made spontaneously without advance preparation
A short musical composition for an informal occasion often with the character of improvisation and usually to be played solo.
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"
Improvised; without prior preparation, planning or rehearsal.