Impromptu vs Improvise - What's the difference?

As an adjective impromptu

is improvised; without prior preparation, planning or rehearsal; extemporaneous; unplanned.

is a short musical composition for an informal occasion often with the character of improvisation and usually to be played solo.

to make something up or invent it as one goes on; to proceed guided only by imagination, instinct, and guesswork rather than by a careful plan.

(-)

Improvised; without prior preparation, planning or rehearsal; extemporaneous; unplanned.

The party began with an impromptu rendition of 'Happy Birthday'.

* See also

(en noun)

(music) a short musical composition for an informal occasion often with the character of improvisation and usually to be played solo.

any composition, musical or otherwise, that is created on the spot without preparation.

To make something up or invent it as one goes on; to proceed guided only by imagination, instinct, and guesswork rather than by a careful plan.

He had no speech prepared, so he improvised .

They improvised a simple shelter with branches and the rope they were carrying.

She improvised a lovely solo.

* fly by the seat of one's pants, play by ear, punt, think on one's feet, wing it

* improvisation * improvisational