This is the 3303rd most frequent Russian word.
отца
"Отца" means "father" (genitive or accusative case) in English.
In this sentence, 'отца' is the direct object of the verb 'видел', indicating the person who was seen.
Я видел отца на улице.
I saw my father on the street.
Here, 'отца' serves as the direct object of the verb 'угощали', referring to the person who is the recipient of the pies.
Мы угощали отца пирогами.
We treated our father with pies.
In this case, 'отца' is used in the genitive case, showing possession to indicate that the guests are father’s friends.