an acquaintance that is only spoken to when all of one's real friends are absent.
A: Why were you talking to Erik that other day?
B: Dude, he's just a back-up friend. nobody else was around worth talking to.
someone you are friends with, but doesn't make the list(first cut, VIP, ect) for an activity, and then is called upon to fill in when a "Real friend" cannot be there
1)Hey did you enjoy the party?
Nah, i didn't know there was one.:(
Oh that's right, because you're a BACK-UP FRIEND! HAHA
2) Hey man, i can't make it tonight. Call Drew, you know he doesn't have any real friends.
Hey Drew wanna come to the party tonight?
YEAH SURE MAN, THANKS FOR INVITING ME.
A friend who isn't really part of the group, but who you hang out with when the rest of the group is gone.
Why isn't Kailyn paying any attention to Meggie?
Oh, Meggie's just her back-up friend. She's talking to Ashley right now.