So this is the vocative case in Romanian? Is there any lesson on Duolingo to teach us this case? Or should I search it from another source?
Why is this expression in the genitive-dative form?
Edit: Thanks to those who downvoted my (obviously stupid) question. And many thanks to Enchom who explain everything, even in detail!
Actually, beside nominative-accusative and dative-genitive, Romanian also has a fifth case called vocative case, which is used when you are addressing someone/something. In the vocative case all plural nouns take the ending -lor, so I believe that is what is used in this expression. Wikipedia has some good information about the vocative case in Romanian :)