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.
by assgoblin82 January 31, 2007
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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.
by Sleet October 23, 2009
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a hostile directive to retreat; usually to feign an attempt to prevent an altercation.
Nigga, You had best to back the fuck up offa me fo I beat yo bitch-ass!
by spence-doggy-ddog February 1, 2006
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Person you invite to go somewhere when your preferred person cannot go. Can be male or female (non-gender specific).
"You can't make it? I better call my back-up bitch!"
by Rob Norment March 30, 2007
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when a girl puts that delightful arch in her back, and sticks her ass out in a erotic/sexually suggestive manor, often accompanied by a "booty dance", that brings shear delight to the males species.
"did you see her back that ass up, playboy? it almost brought a tear to me eye, and a 2x4 to my pants!"

"did you see lucy liu bending over in the drive-thru scene in charlies angels?? ddaaaaaaaaamn, it was delightful! that the essence of female perfection!"
by deluks November 30, 2005
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There are usually "back-up channels" in which to people use in times when all other channels are on adverts. This saves people from being bored and changing activity to going outside or reading.
Dude - "I'm so glad we have this back-up channel.. i mean police camera action is pretty boring but i'm glad we're not watching some shitty adverts.
Dude-et - "yeah the adverts these days are just all for freakin injury lawyers.."
by Jonny Clarke July 5, 2009
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