A more thorough explanation:

Term: in promptu
Definition: In promptu means "at hand" in Latin. It is an old-fashioned word that means impromptu. It refers to something that is done without preparation or planning.
Examples: When the teacher asked him to give a speech, he gave an impromptu speech. The singer sang an impromptu song at the party.
Explanation: The examples show situations where something is done without preparation or planning. The speaker gave a speech without preparing for it, and the singer sang a song without planning it beforehand. Both situations illustrate the meaning of in promptu.