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When a gym rat flexes his back muscles giving off the appearance of a butt crack
Colin is such a frat star flexing his back butt.
by Collin has backbutt August 05, 2016
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When a girl has large dimple like indentations on her lower back directly above her butt. This results in a sometimes sexy, strange occurance called the back butt.
"Damn, I don't know wether to be turned on or throw up at the sight of Lexxy's back butt."

"I hate summer. I don't like to show off my back butt. Seriously, aren't dimples supposed to be on your face?"
by ShaIchLuge July 10, 2008
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This is when you can't tell the difference in a girl's back from her butt. Flat butt, pancake butt.
She got a backbutt.
by anRobot April 05, 2017
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