Shirin (شیرین) is the Persian word for "sweet." The romance of Khosrow and Shirin by the 12th-century poet Nizami is one of the great Persian love stories.
Shirin 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 Shirin reduce to 5, The Seeker. This is a traditional interpretive system, not a factual claim about the name.