Thalia (Θάλεια) comes from the Greek thallein, meaning "to bloom" or "to flourish." In Greek mythology, Thalia is the muse of comedy and idyllic poetry — one of the nine daughters of Zeus and Mnemosyne.
Thalia entered the U.S. top 1000 in 1992 and has been continuously used.
Thalia 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 Thalia reduce to 6, The Nurturer. This is a traditional interpretive system, not a factual claim about the name.