Improvisation (from the Latin improvisus, “unforeseen”; ex improvisio, “without preparation”) in music denotes simultaneous invention and realization in sound. Already occasionally used in medieval music theory, the term was included in Jean-Jacques Rousseau’s 1768 Dictionnaire de musique. However, it seems to have prevailed over other terms, such as “impromptu”, “fantasia”, “extemporization,” or “preludization,” only around the middle of the 19th century.