It can be used toward each other amongst lovers, family, friends and even sometimes strangers in a joking or "light-hearted" manner, depending on the context and how its used in the Spanish speaking country of origin where the person saying it is from.
It can be equivalent to saying "honey", "hun", "sweetie", "babe", "baby", etc.
Husband: "Exhausting.. I'm tired and hungry. What's for dinner mami?"
Mom: "Hurry up and get ready for school nene. You're gonna be late!"
Son: "But I don't feel so good. I think I'm sick" *coughs*
Friend (guy): "Damn, look at Carmen.. She's so fly."
Friend (girl): "You still crushin' on her nene? Man, you've liked her since 6th grade! Why don't you just ask her out??"
Cash register older lady: "Find everything in the store ok nene?"
Kid: "Yes Ma'm"