This is the 57th most frequent Latvian word.
viņu
"Their" or "them" (possessive or objective pronoun).
In this sentence, 'viņu' functions as a third-person singular masculine or feminine pronoun in the accusative case, used to refer to a person as the direct object.
Es redzēju viņu parkā.
I saw him/her in the park.
Here, 'viņu' is used as a third-person plural pronoun in the accusative case, indicating them as the direct object of the verb.
Mēs apmeklēsim viņu nākamnedēļ.
We will visit them next week.
In this example, 'viņu' acts as a third-person plural possessive pronoun, describing ownership of the book.