Coucou!

I keep hearing my French roommate say, "Coucou!" to her friend (who lives in the flat across the hall from us), and it's so cuteeee!!!! and I kept wondering what it meant, so one day when I knocked on the flat door, and my roomie's friend opened it, I said, "Coucou!" and my roomie, who was also there heard me and she said it was so cute that I said it- and it sounds so fun, right? So I finally found out (altho that's what my guess was) that "Coucou" is a informal, more friendly way of saying "Hi"...

Oh and "À tout à l'heure", or "Tout alors", means "See you later" too....