Elsa is the German short form of Elisabeth — from the Hebrew Elisheba, meaning "my God is an oath." The name has been used across Germanic Europe for centuries.
Elsa rose dramatically in the U.S. after Disney's Frozen (2013), in which the Snow Queen Elsa is the central character. Today it sits in the U.S. top 200.
Elsa 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 Elsa reduce to 1, The Leader. This is a traditional interpretive system, not a factual claim about the name.