Aileen is the Scottish and Irish form of Helen — from the Greek helios (sun), meaning "bright" or "shining." Also linked to the Old German Adelina (noble).
Aileen Hernandez (1926-2017) was the American civil rights leader. Aileen Wuornos (1956-2002) was the convicted American serial killer.
Aileen 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 Aileen reduce to 1, The Leader. This is a traditional interpretive system, not a factual claim about the name.