Tess is the English short form of Theresa or Teresa — from the Greek therizō, meaning "to harvest" or "to reap." Thomas Hardy's Tess of the d'Urbervilles (1891) made Tess a tragic literary icon.
Tess has been continuously used since the 19th century. Today it sits in the U.S.
Tess 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 Tess reduce to 9, The Giver. This is a traditional interpretive system, not a factual claim about the name.