(adj)
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 soundoffhanded and reassuring"; "an off-the-cuff toast"; "a few unrehearsed comments"
(adv)
without advance preparation; "he spoke ad lib"