Selen is the Turkish word for "waterfall" or "abundant rushing water" — also the name of the Selenga River that flows from Mongolia into Lake Baikal. A modern Turkish feminine name.
Selen Soyder (born 1985) is the Turkish actress.
Selen 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 Selen reduce to 1, The Leader. This is a traditional interpretive system, not a factual claim about the name.