Marni comes from the Hebrew Marnina, meaning "rejoice," or from Marina (Latin "of the sea"). The name is also associated with Marni Nixon, the singer who dubbed Audrey Hepburn in My Fair Lady.
Marni is rising as part of the broader vintage revival.
Marni 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 Marni reduce to 1, The Leader. This is a traditional interpretive system, not a factual claim about the name.