Felicitas is the Latin word for "happiness" or "good fortune" — personified as the Roman goddess of luck. Saint Felicitas of Carthage (d. 203) was a 3rd-century martyr.
Felicitas is widely used in Germany and Italy.
Felicitas 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 Felicitas reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.