Tosca is from the Italian Tosca — "Tuscan, from Tuscany" — a regional epithet that became a feminine given name through Sardou and Puccini's operatic heroine. Tosca is also a popular Italian café-restaurant brand and a top-500 Italian girl's name in the 2020s.
Tosca 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 Tosca reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.