Diễm (艷) is the Vietnamese word for "charming" or "alluring beauty" — from the same root as Chinese yàn.
Diem is widely used in Vietnam.
Diễm 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 Diễm reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.