Oana is from the Romanian Oana — Romanian rendition of Joanna / Ioana — from the Hebrew Yochanan (Yahweh is gracious). Oana is one of the Romanian feminine names.
Oana 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 Oana reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.