Tessa is the short form of Theresa (also spelled Teresa) — itself of disputed etymology, possibly from the Greek therizein, meaning "to harvest," or from theros (summer), or even from the Greek island of Therasia.
Tessa entered the U.S. top 1000 in 1981 and has been climbing steadily. Today it sits in the U.S. top 250.
Tessa 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 Tessa reduce to 1, The Leader. This is a traditional interpretive system, not a factual claim about the name.