it means "hey", it's a word used to get attention, the whole sentence is: hey, why didn't you come to the party the day before yesterday?

類似漢語里的”嘿，小白“ ”黑，老兄” “喂！”

It's similar to "hey" in English, but It's quite informal and usually rude. In English it's literally "hear".

in chinese it means 喂,嘿,语气词

hi :D ... in spanish .. is like a : "hey you" ... or " pay attention ".....