IPA: /ɛkˌstɛmpəraɪˈzeɪʃən/
KK: /ɛkˌstɛmpəraɪˈzeɪʃən/
The act of speaking or performing without preparation or planning, often in a spontaneous manner.
His extemporisation during the debate impressed everyone in the audience.
Extemporisation → It is formed from "ex-" (meaning out of) and "temporarius" (from Latin, meaning temporary or of time). The word refers to the act of speaking or performing without preparation, as if one is drawing from the moment or the time at hand.
Think of 'drawing out' ('ex-') from the 'moment' ('temporarius') — that's why extemporisation means to perform or speak spontaneously.