This is the 6889th most frequent Russian word.
азербайджану
"Азербайджану" means "to Azerbaijan" (dative case of "Азербайджан").
In this sentence, 'Азербайджану' is used in the prepositional case to denote location or area of the travel.
Я путешествовал по Азербайджану в прошлом году.
I traveled around Azerbaijan last year.
Here, 'Азербайджану' is in the dative case indicating the destination of the action.
Мы отправили письмо в Азербайджану.
We sent a letter to Azerbaijan.
In this example, the word 'Азербайджану' is in the prepositional case used to refer to the subject matter.