What is "ainulindale"

Ainulindalë (; "Music of the Ainur") is the creation account in J. R. R. Tolkien's legendarium, published as the first part of the posthumously published The Silmarillion (1977).

In many ways central to Tolkien's " subcreative" cosmology, the Ainulindalë gives an account of the Ainur, a class of angelic beings, who perform a great music prefiguring the creation of the material universe ( Eä). Ilúvatar introduces the theme of the sentient races of Elves and Men, not anticipated by the Ainur, and gives physical being to the prefigured universe. Some of the Ainur decide to enter the physical world to prepare for their arrival, becoming the Valar.

Tolkien wrote the initial version of "Ainulindalë" from November 1919 to the spring of 1920 as "Music of the Ainur", completely rewriting it in 1930. After further revisions by the author, it was published by his son Christopher in The Book of Lost Tales (the first two volumes of The History of Middle-earth).