Serena comes from the Latin serenus, meaning "clear" or "tranquil" — referring originally to the sky. The English "serene" derives from the same root. The name has been used since ancient Rome.
Today Serena sits in the U.S. top 250.
Serena 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 Serena reduce to 8, The Visionary. This is a traditional interpretive system, not a factual claim about the name.