Cleo is a bright, economical short form of Cleopatra, the Greek name meaning "glory of the father," borne most famously by the last queen of Ptolemaic Egypt.
Cleo 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 Cleo reduce to 8, The Visionary. This is a traditional interpretive system, not a factual claim about the name.