Bach's title for 30 short imitative keyboard works (from 1720-23) in two and three parts. While Vitali and Bonporti also used the term "invention," their works are very different; today the term is used almost exclusively in reference to Bach.
fairly short keyboard piece
In music, an invention is a short composition (usually for a keyboard instrument) with two-part counterpoint. (Compositions in the same style as an invention but using three-part counterpoint are known as sinfonias. Some modern publishers are erroneously calling them "three-part inventions" to avoid confusion with symphonies.)