Joy is the English word — from the Old French joie, from the Latin gaudia, meaning "joys" or "delights." It became a Puritan virtue name in the 17th century, joining Faith, Hope, and Grace as direct word-names given to daughters.
Joy entered the U.S. Today it sits in the U.S. top 350 and is rising — short, direct, with no need for explanation.
Joy 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 Joy reduce to 5, The Seeker. This is a traditional interpretive system, not a factual claim about the name.