Petra is the feminine of Peter — from the Greek petros (πέτρος), meaning "rock" or "stone." Jesus called Simon "Cephas" (Aramaic for rock), which was translated into Greek as Petros (Peter). Petra is also the name of the ancient rose-red city carved into rock cliffs in southern Jordan, now a UNESCO World Heritage Site.
Petra is widely used across Eastern Europe (especially Czech Republic, Slovakia), Germany, Scandinavia, and parts of South America. In the U.S. it sits in the top 800 and is rising. The Czech tennis player Petra Kvitová is a famous bearer.
Petra 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 Petra reduce to 6, The Nurturer. This is a traditional interpretive system, not a factual claim about the name.