Idunn (Iðunn) is the Old Norse goddess of youth and immortality — keeper of the golden apples that gave the gods their eternal youth. Wife of the poet-god Bragi.
Idunn is widely used in Scandinavia.
Idunn does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Idunn reduce to 8, The Visionary. This is a traditional interpretive system, not a factual claim about the name.