This is the 705th most frequent Romanian word.
fusese
"Fusese" is the past perfect form of "to be" in Romanian, meaning "had been."
The word 'fusese' is used here to indicate that the action of 'leaving' was completed before another past action ('arrived'). This is an example of the pluperfect tense.
El fusese deja plecat când am ajuns.
He had already left when I arrived.
In this sentence, 'fusese' shows that 'being a teacher' is an action completely occurred before the subsequent past action ('retiring').
Ea fusese profesoară înainte de a se pensiona.
She had been a teacher before retiring.
The verb 'fusese' here is used to express the completion of the state of 'being at the party' before the moment of 'thinking' in the past.