Cassia comes from the Latin (and Greek kasía) name for the cinnamon tree — a fragrant spice tree whose bark and oil have been valued since antiquity.
Cassia is rising fast in the U.S.
Cassia 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 Cassia reduce to 7, The Seeker. This is a traditional interpretive system, not a factual claim about the name.