Hallway Hello Friend
Someone you know who isn't really your friend, but who you say hello to when you see them pass by. This term usually defines someone who you don't really know that well or who you don't really hang out with, but is someone who you would greet in passing.
Person 1: "Kelly Smith. Do you know her?"
Person 2: "Sorta. She was more of a hallway hello friend"
Person 2: "Sorta. She was more of a hallway hello friend"