An impromptu (pron.: //, French: [ɛ̃prɔ̃pty], 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.
Form Usage 
Since the very concept of unpremeditated, spur-of-the-moment inspiration without studied care is at the heart of Romantic artistic theory, it did nоt take long before the first generation of Romantic composers took up the idea:
- Jan Václav Voříšek was the first one to compose impromptus published under that title, in 1822.
- Franz 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.
- Frédéric 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.
- Alexander Scriabin is known to have written at least nine impromptus for the piano in his early period.
- Jean Sibelius composed six impromptus for piano op. 5 (1893)
The impromptu genre remained popular all throughout the 19th century.
In the 20th century, there are also several examples of composers naming their compositions "Impromptu", such as:
- Gabriel Fauré composing six Impromptus between 1881 and 1913.
- Richard Rodney Bennett composing five Impromptus for guitar in 1968
- Maurice Journeau composing six Impromptus between 1971 and 1974.
- Donald Martino composing Fantasies and Impromptu in 1980.
- Nikolai Kapustin composing four Impromptus between 1991 and 1997.
- Lowell Liebermann composing Three Impromptus Op.68 in 2000.
- Vince Mendoza's Epiphany, performed by the London Symphony Orchestra and published in 1999. The first piece of the album is named Impromptu.
- One of Queen's compositions, performed at Wembley Stadium and other performances is named Impromptu.