This is the 11848th most frequent German word.
theresia
"Theresia" is a German feminine given name, equivalent to "Theresa" in English.
Here 'Theresia' is used as a proper noun, referring to a person's name.
Theresia ist eine gute Freundin von mir.
Theresia is a good friend of mine.
In this sentence, 'Theresia' is again a proper noun, referring to the person's name in a possessive context.
Wir bewundern den Mut von Theresia.
We admire Theresia's courage.
Here 'Theresia' is referring to 'Saint Theresa', used as a proper noun within a religious context.