An impromptu (loosely meaning "offhand") is a free-form musical composition with the character of an improvisation, usually for a solo instrument, such as piano. (Not prepared or unrehearshed)

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 Voříšek.

It didn't take long before the first generation of Romantic composers took up the idea:

• J. H. Worzišek was the first one to compose impromptus, in 1822.
• Schubert published two sets of four Impromptus for piano op. 90 and 142 (1827). After his death 3 more unnamed piano compositions (Klavierstücke) were sometimes named Impromptus.
• Chopin composed 4 Impromptus, including the famous Fantaisie-Impromptu.
• Robert Schumann wrote some Impromptus, published as Op. 5.
• Franz Liszt composed an Impromptu in F sharp (sometimes called Nocturne) and a piano piece named Valse-Impromptu.
• Jean Sibelius composed six pompromptus for piano op. 5 (1893)

The impromptu genre remained popular all throughout the 19th century.

In the 20th century there are fewer examples of composers naming their compositions "Impromptu", e.g.:

• Donald Martino composing Fantasies and Impromptu in 1980.
• One of Queen's compositions, performed at Wembley Stadium in 1986 is named Impromptu.

References

• New Grove Dictionary of Music and Musicians