Since it is a diminutive of Theresa/Teresa it means the same thing and under
Theresa it says:
"From the Spanish and Portuguese name
Teresa. It was first recorded as
Therasia, being borne by the Spanish wife of Saint
Paulinus of
Nola in the 4th century. The meaning is uncertain, but it could be derived from Greek θερος (theros) "
SUMMER", from Greek θεριζω (therizo) "TO HARVEST", or from the name of the Greek ISLAND OF
THERASIA (the western island of Santorini).
The name was mainly confined to Spain and Portugal during the Middle Ages. After the 16th century it was spread to other parts of the
Christian world, due to the fame of the Spanish nun and reformer Saint
Teresa of Ávila. Another famous bearer was the Austrian Habsburg queen
Maria Theresa (1717-1780), who inherited the domains of her father, the Holy
Roman Emperor
Charles VI, beginning the War of the Austrian Succession."