Gemma is the Italian word for "gem" or "precious stone" — from the Latin gemma, meaning "bud" or "jewel." Saint Gemma Galgani (1878-1903), an Italian mystic, was canonised in 1940.
Gemma is one of the most popular girl names in Italy and the United Kingdom. In the U.S. it entered the top 1000 in 2007 and has climbed steadily. Today it sits in the U.S. top 175.
Gemma 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 Gemma reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.