the act of wen a guy is sitting on the ground, bed, or couch with his legs spread and his girfriend or otherwise sits leaning against him sitting just so her back lays right in the crook of his crotch. this usualy causes the guy 2 develop a boner.
I saw kyle poking his dick into julie's back! haha! they where having some hot backsex!!!
by penelopedark<3 October 03, 2010
Slang for "anal sex", "buttsex", etc.
She won't let me have back sex because she's afraid it will hurt.
by Raddue December 12, 2005

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