Pelagia (Πελαγία) is the Greek word for "of the sea" — from pelagos (open sea). Saint Pelagia of Antioch was the early Christian convert (5th c.) who, after a life as a famous courtesan, retreated to Mount Olives in male disguise and lived as an ascetic until her death.
Patron saint of penitents.
Pelagia 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 Pelagia reduce to 6, The Nurturer. This is a traditional interpretive system, not a factual claim about the name.