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1.
A large, curvy womans ass , or the rear profile of a woman with a very generous rear view of her larger than normal buttocks.

Usually associated with the hour glass figure type of woman, where the ass is suprisingly large.
Did you see the back porch on her? The term "back porch" is over emphasized in a conspiratorial tone of voice, to ensure that the listener understands that one is referring to a womans body.
by 415man94102 June 03, 2006
 
2.
Verb. To take a shot by having it poured down the back and ass crack of a man, usually after losing a bet.
My mouth is on fire after back porching fireball.
by Hot shot December 16, 2013