Nessa is from the Hebrew נֵס (Nes — miracle, sign, banner) — with diminutive feminine ending. Nessa is one of the Hebrew feminine names — central to traditional Jewish heritage.
Nessa 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 Nessa reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.