This is the 9754th most frequent Russian word.
эдуарду
"Эдуарду" is the dative case of the male name "Эдуард" (Eduard), meaning "to Eduard" or "for Eduard" in English.
Here, "Эдуарду" is in the dative case, used to signify the indirect object of the action, i.e., to whom the letter is addressed.
Я написал письмо Эдуарду.
I wrote a letter to Eduard.
In this sentence, "Эдуарду" is again in the dative case, showing to whom the book was given as a gift.
Мы подарили книгу Эдуарду.
We gave a book to Eduard.
Here, "Эдуарду" is used in the dative case to indicate the person to whom the question is directed.