Idun (Iðunn) is the Norse goddess of youth and renewal — keeper of the golden apples that gave the gods their immortality. Her name means "the rejuvenating one" or "ever young."
Idun is rare as a given name but used in modern Scandinavia.
Idun 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.
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In Pythagorean numerology the letters of Idun reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.