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1.
1) having guts or balls

2)the "behind the scenes" guy(s) of an outfit or group who do a signficant contribution to something but don't get as much recognition. Second only to the heart and soul.
1) You've got to grow a backbone if you don't want to become the one who gets trampled over in the end.

2) If she's the heart and soul of the group, then those two are the backbone of it.
by Lazy T May 18, 2009
 
2.
Individuals who make a substantial contribution to a team/event/organisation. Without them the whole thing would fall apart.
Jay Robinson is the Backbone of 4Marketing
Perry Padina is the Backbone of FCC Paragon
by The R Rated Superstar December 19, 2013
 
3.
slang term for arse.
you need to let me behind ya backbones
by Bullet_NvA September 15, 2008
 
4.
The sometimes pleasureful event in which a male becomes erect while spooning with a female.
Dude, last night I got a backbone while spooning with Charlotte! It was awkward at first, but then she started using her spine to rub my erect manhood!
by Ballzach July 09, 2012