This is the 879th most frequent Bulgarian word.
трета
"Трета" in English means "third."
The word 'третия' is the masculine form of 'third,' used here as a descriptor for the 'floor'.
Той живее на третия етаж.
He lives on the third floor.
The word 'третата' is the feminine form of 'third,' indicating her position in the list.
Тя е третата в списъка.
She is the third on the list.
Here 'третата' is again the feminine form of 'third,' describing the specific word to be repeated.