What is the term for an unprepared speech?

The correct term for an unprepared speech is "impromptu." An impromptu speech occurs when a speaker is given little or no time to prepare before speaking. This type of speech relies on the speaker's ability to think quickly and articulate their thoughts spontaneously. It assesses the ability to respond effectively in the moment, making it a valuable skill in many situations, such as discussions or debates.

Prepared speeches, on the other hand, involve prior organization of thoughts and ideas, which is not the case for impromptu speaking. Extemporaneous speeches typically involve some preparation, usually with a limited amount of time to organize thoughts beforehand, making them more structured than impromptu speeches. Scripted speeches, as the name suggests, involve delivering a pre-written text, which is the opposite of being unprepared. Thus, the essence of impromptu speaking lies in its spontaneity and the speaker's immediate engagement with the topic.