Clémence is the French form of Clemence — from the Latin clementia, meaning "mildness" or "mercy." Saint Clemence of Hohenburg was the medieval abbess.
Clémence Poésy (born 1982) is the French actress known for Fleur Delacour in Harry Potter.
Clémence 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 Clémence reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.