This is the 8694th most frequent Russian word.
парфенову
"Парфенову" is not a standalone word but a surname in the dative case in Russian, meaning "to Parfenov" or "for Parfenov."
Here, 'Парфенову' is in the dative case, indicating the indirect object of the action—whom the letter was handed to.
Вчера я передал письмо Парфенову.
Yesterday I handed the letter to Parfenov.
In this sentence, 'Парфенова' is in the accusative case, as it is the direct object of the verb 'видели' (saw).
Мы видели Парфенова на концерте.
We saw Parfenov at the concert.
In this context, 'Парфенова' is in the genitive case, showing possession.