Remark made spontaneously without prior preparation.

Perform without preparation.

synonyms: extemporise, extemporize, improvise, improvize.

Dutch: improviseren

With little or no preparation or forethought:
— His ad-lib comments showed poor judgment.

synonyms: extemporaneous, extemporary, extempore, impromptu, off-the-cuff, offhand, offhanded, unrehearsed.

Said or done without having been planned or written in advance:
— He made a few ad-lib remarks.

synonyms: spontaneous, unwritten.

Polish: spontaniczny