off-the-cuff

/AO1 F DH AH0 K AH1 F/
adjective
  1. 1

    Extemporaneous; without prior preparation; spontaneous; impromptu.

    โ€œHe made a few off-the-cuff remarks before launching into his prepared speech.โ€

Source: https://en.wiktionary.org/wiki/off-the-cuff