This is the 9th most frequent Romanian word.
au
"Au" means "have" (third person plural, present tense) in English.
In this sentence, 'au' is the present tense of the verb 'a avea' (to have), indicating possession.
Ei au o pisică albă.
They have a white cat.
Here, 'au' is used as an auxiliary verb in the past tense form to construct the past tense together with the main verb 'găsit'.
Copiii au găsit niște flori în parc.
The children found some flowers in the park.
In this context, 'au' acts as an auxiliary verb to form the past tense of the compound verb 'au trecut' within the sentence.