Leocadia comes from the Greek leukos (white, bright). Saint Leocadia of Toledo (died c. 304 CE) was a Spanish virgin martyr; the cathedral of Toledo is built on her feast day site.
Leocadia is widely used in Spain, Portugal, and Latin America. Goya painted Leocadia Weiss, his late-life companion.
Leocadia 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 Leocadia reduce to 5, The Seeker. This is a traditional interpretive system, not a factual claim about the name.