The word "impromptu" refers to something that is done without preparation or planning. It often describes a spontaneous action or event that is created or performed on the spur of the moment. For example, an impromptu speech might be delivered without any notes or prior rehearsal, simply arising from the need to say something in that moment.
The term "impromptu" comes from the late Latin phrase "impromptus," meaning "unforeseen." It evolved from the Latin verb "promptus," which means "to bring to light" or "ready." The word took on its current meaning in English in the 18th century, describing actions or performances executed without prior arrangement.