To get on someone's back, wrap your arms and legs like straps around the person and hide your head in their shoulder, like a backpack. AKA the newplanking.
slang for a gay males having sex...anal sex...How one would be behind the other person with his arms and hands over his shoulder thereby being like on wearing a backpack.
Like scissoring for Lesbians.
Aw...those guyslook like they are going backpacking!