Miley is a modern American name — invented as a contraction of "Smiley" by Miley Cyrus's family (her birth name was Destiny Hope Cyrus, and "Smiley" was her father Billy Ray's nickname for her). A top-500 US baby name since 2007.
Miley 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 Miley reduce to 1, The Leader. This is a traditional interpretive system, not a factual claim about the name.