Liisa is the Estonian and Finnish form of Elizabeth — Hebrew Elisheba, "pledged to God." One of the most common Estonian feminine names.
Used widely in Estonia and Finland.
Liisa 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.
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In Pythagorean numerology the letters of Liisa reduce to 5, The Seeker. This is a traditional interpretive system, not a factual claim about the name.