When a girl/guy is standing up, a guy/girl would come behind them, and wrap his/her arms around their stomach, (also known as a backwards hug. This usually happens in a loving way, however it can also be determined in a rape fashion.
An action where in the middle of a hug the guy lowers his hands around the girl's ass, creating a swing for the girl to lean on, this has a very deep meaning for the girl, it means that for the girl, the guy will always be there for her. And for the guy, it's just another way to feel up a girl.
"Awww, look at that couple, they haven't seen each other for so long, I'm gonna go over there and say hi."
"No don't!! They're in the middle of an ass hug, this is important for their relationship!"