Medusa is from the Greek Médousa (Μέδουσα — guardian, protectress). Medusa in Greek mythology is the iconic Gorgon, central to Hesiod's Theogony (c. 700 BCE) and Ovid's Metamorphoses (8 CE).
Medusa 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.
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In Pythagorean numerology the letters of Medusa reduce to 9, The Giver. This is a traditional interpretive system, not a factual claim about the name.