Réka was the wife of Attila the Hun (mother of his eldest sons). The name possibly comes from the Hungarian rege, meaning "legend" or "saga."
Réka is widely used in modern Hungary.
Réka 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 Réka reduce to 5, The Seeker. This is a traditional interpretive system, not a factual claim about the name.