In Norse mythology, Iðunn is the goddess associated with apples and youth. Iðunn is attested in the Poetic Edda, compilled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturluson. In both sources, she is described as the wife of the skaldic god Bragi, and in the Prose Edda, also as a keeper of apples and granter of eternal youthfulness.
The lyrics of this song are taken from the poem Hrafnagaldr Óðins (Odin's Raven Magic):
"Dvelur í dölum Dís forvitin Yggdrasils frá Aski Hnigin Álfa ættar Idunni hétu Ívalds eldri Yngsta barna"