Temperancia represents the virtue of Temperance, one of the four Cardinal Virtues. The word 'cardinal' derives from the Latin cardo which means 'hinge', as the virtues were understand as the hinges opening the entry to morality. Taken from Plato's system outlined in his 'The Republic', church men like St. Augustine and Thomas Aquinas took the virtues as 'good qualities of mind whereby we live righteously' (and strangely omitted Plato's fifth virtue, Piety'...)
Temperance is the virtue of moderation and of balance. We'll find her in almost every traditional Tarot deck, as Temperance, or in the Crowley deck as 'Art'. Her 'trademark' are the two vases from which she pours a liquid from one vase into the other. She is often seen accompanied by a dog.