The fictional account describing Númenor’s destruction in J.R.R. Tolkien’s legendarium is titled Akallabêth.
Akallabêth is one of the principal sections of The Silmarillion. It tells how the island kingdom of Númenor, founded for the ancestors of the Dúnedain, grew powerful and wealthy before its rulers became increasingly resentful of the immortality of the Elves and fearful of death.
Under King Ar-Pharazôn, Númenor challenged the authority of the Valar. The island was destroyed when Ar-Pharazôn attempted to invade the Undying Lands. The catastrophe changed the shape of the world, while Elendil and other faithful Númenóreans escaped and later founded kingdoms in Middle-earth.
Akallabêth is a title in Tolkien’s invented Adûnaic language and is commonly translated as “The Downfallen.” It is not the same as Ainulindalë, the creation account, or Valaquenta, which describes the Valar and Maiar.