Lily is the English name of the flower, ultimately from the Latin lilium. In Christian symbolism, the white lily represents purity and is closely associated with the Virgin Mary; in classical mythology, the lily sprang from drops of Hera's milk. The name's modern use derives from the flower rather than from any earlier given name.
Today it sits in the U.S. top 30 and is consistently in the top 5 in the United Kingdom.
Lily 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 Lily reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.