IPA: /ɛkˌstɛmpəraɪˈzeɪʃən/
KK: /ɛkˌstɛmpəraɪˈzeɪʃən/
The act of speaking or performing without preparation or planning, often in a spontaneous manner.
His extemporization during the speech impressed the audience with its creativity.
Extemporization → It is formed from "ex-" (meaning out of or from) and "temporarius" (from Latin, meaning temporary or of time). The word refers to the act of speaking or performing without preparation, thus coming from a place of immediacy or spontaneity.
Think of 'coming from' ('ex-') a 'temporary' moment ('temporarius') — that's why extemporization means to perform or speak spontaneously.