Flossie is the English diminutive of Florence — ultimately from the Latin florere ("to flower, to bloom"). Flossie Mae Hunter — American activist. Flossie also appears as a popular dairy-cow name across American and English farming traditions — the cows of Roald Dahl's Fantastic Mr. Fox (1970) include Flossie. The name is currently undergoing a vintage-revival as one of the -ie / -y feminine diminutives along with Birdie, Sadie, Nellie, and Lottie.
Flossie 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 Flossie reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.