Fanny is the English diminutive of Frances — from the Latin Franciscus ("Frenchman, free one"). A top-100 US baby name from 1880 to 1899; outside the US, the name remains common in France, Sweden, and Latin America. Fanny Lu — Colombian pop singer. The name has fallen out of common US use but remains widely loved in Continental Europe.
Fanny 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 Fanny reduce to 6, The Nurturer. This is a traditional interpretive system, not a factual claim about the name.