Cassandra comes from the Greek Kassandra (Κασσάνδρα), traditionally interpreted as "she who shines upon men" or "shining over men." In Greek mythology, Cassandra was the Trojan princess gifted with prophecy by Apollo but cursed never to be believed — she foresaw the fall of Troy but no one listened.
Cassandra peaked at #65 in 1990 and has been declining since. Today it sits in the U.S. top 500.
Cassandra 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 Cassandra reduce to 8, The Visionary. This is a traditional interpretive system, not a factual claim about the name.