Effy is the English diminutive of Euphemia — from the Greek eu-phēmia ("fair speech, good repute"). Saint Euphemia of Chalcedon (died c. Euphemia in Chalcedon was the site of the 451 CE Council of Chalcedon — one of the most-important early Christian councils, which defined Christological doctrine for centuries. Effy Howson — British comedian. The name's modern revival through Skins has made Effy and Effie (alternate spelling) popular indie-British naming choices.
Effy 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 Effy reduce to 6, The Nurturer. This is a traditional interpretive system, not a factual claim about the name.