Ainulindalë is the title Tolkien gave the first part of the mythology later published in The Silmarillion.
Ainulindalë, meaning “The Music of the Ainur,” describes the creation of the world through a great musical theme conceived by Eru Ilúvatar and performed by the Ainur. The section introduces the cosmic conflict involving Melkor and establishes the mythic origin of Arda, the world in which Middle-earth exists.
The Silmarillion is divided into major sections with different purposes. Valaquenta describes the Valar and Maiar, Quenta Silmarillion recounts the history of the Silmarils and the First Age, and Akallabêth tells of Númenor. Ainulindalë is therefore not another name for the whole book or its central historical narrative; it is the opening creation account. The work was published posthumously in 1977 under Christopher Tolkien’s editorship.