Jocelyn comes from the medieval Old French Joscelin — itself from the Germanic Gauzlin, referring to a member of the Gauts (an East Germanic tribe). It was originally a masculine name; English usage made it predominantly feminine.
Jocelyn entered the U.S. top 1000 in 1942 and has risen steadily. Today it sits in the U.S. top 200.
Jocelyn 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 Jocelyn reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.