Aleatoric music (also aleatory music or chance music; from the Latin word alea, meaning "dice") is music in which some element of the composition is left to chance, and/or some primary element of a composed work's realization is left to the determination of its performer(s). The term is most often associated with procedures in which the chance element involves a relatively limited number of possibilities.
The term became known to European composers through lectures by acoustician Werner Meyer-Eppler at the Darmstadt International Summer Courses for New Music in the beginning of the 1950s. According to his definition, "a process is said to be aleatoric ... if its course is determined in general but depends on chance in detail" (Meyer-Eppler 1957, 55). Meyer-Eppler's German terms Aleatorik (noun) and aleatorisch (adjective), however, both mean "aleatory". By mistakenly rendering them, his translator inadvertently created a new English word, "aleatoric", which quickly became fashionable (Jacobs 1966). More recently, the variant "aleatoriality" has been introduced (Roig-Francolí 2008, 340).