[adj ]: spoken, performed done, or composed with little or no preparation [Elements of Plot] Inciting force [noun]: the event of character that triggers the conflict [Elements of Plot]
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"
An impromptu action is one that you do without planning or organizing it in advance. This afternoon the Palestinians held an impromptu press conference. done or said without any preparation or planning impromptu speech/party/meeting etc (in promptu )
an extemporaneous speech or remark; "a witty impromptu must not sound premeditated" a short musical passage that seems to have been made spontaneously without advance preparation