Étude

An étude (/ ˈeɪtjuːd/; French pronunciation: ​[eˈtyd], a French word meaning study) is an instrumental musical composition, usually short, of considerable difficulty, and designed to provide practice material for perfecting a particular musical skill. The tradition of writing études emerged in the early 19th century with the rapidly growing popularity of the piano. Of the vast number of études from that era some are still used as teaching material (particularly pieces by Carl Czerny and Muzio Clementi), and a few, by major composers such as Frédéric Chopin, Franz Liszt and Claude Debussy, achieved a place in today's concert repertory. Études written in the 20th century include those related to traditional ones (György Ligeti) and those that require wholly unorthodox technique (John Cage).

Studies, lessons and other didactic instrumental pieces composed before the 19th century are very varied, without any established genres. Domenico Scarlatti's 30 Essercizi per gravicembalo ("30 Exercises for harpsichord", 1738) do not differ in scope from his other keyboard works, and Johann Sebastian Bach's four volumes of Clavier-Übung ("keyboard practice") contain everything from simple organ duets to the extensive and difficult Goldberg Variations.

...
Wikipedia