Aleatoric music

Music in which some element of the composition is left to chance

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, some primary element of a composed work's realization is left to the determination of its performer(s), or both. 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.

From Wikipedia, under CC BY-SA. More on occurri.