Impromptu

An impromptu (/ɪmˈprɒmptjuː/, French: [ɛ̃pʁɔ̃pty], loosely meaning "offhand") is a free-form musical composition with the character of an ex tempore improvisation as if prompted by the spirit of the moment, usually for a solo instrument, such as piano. According to Allgemeine musikalische Zeitung, Johann Baptist Cramer began publishing piano pieces under the (sub-)title of "impromptu." (AMZ, Mar. No II, 1815, col. 6), which seems to be the first recorded use of the term impromptu in this sense.