ad-lib, extemporaneous, extemporary, extempore, impromptu, offhand, offhanded, off-the-cuff, unrehearsed(adverb)

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"

off the cuff(adverb)

without preparation

"the presidential candidate made a remark off the cuff"

off-the-cuff(Adjective)

Extemporaneous; without prior preparation; impromptu.

He made a few off-the-cuff remarks before launching into his prepared speech.