Noun
twelve-tone technique (uncountable)
A system of musical composition devised by Arnold Schoenberg, as a method of composing with twelve notes which are related solely to each other.
In August 1951, just after his first Darmstadt visit, Stockhausen began working with a form of athematic serial composition that rejected the twelve-tone technique of Schoenberg (Felder 1977, 92). Source: Internet
Free atonality The twelve-tone technique was preceded by Schoenberg's freely atonal pieces of 1908–1923, which, though free, often have as an "integrative element. Source: Internet
In August 1927, while staying in Königstein, Copland wrote Poet's Song, a setting of a text by E. E. Cummings and his first composition using Schoenberg's twelve-tone technique. Source: Internet