Impromptu

An impromptu ( /ɪmˈprɒmptjuː/, 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. The first recorded use of the term impromptu in this sense occurred in 1817, in the Allgemeine musikalische Zeitung, an idea of the publisher to describe a piano piece by Jan Václav Voříšek.