The act of vigorously rubbing one's penis in an up and down fashion either between the breasts, or the buttocks, of a woman. This activity is often accompanied by cries of jubilation and triumph in order to further stimulate and encourage the woman to prepare herself for sexual congress.
"Man, I gave her such a solid north-southing last night. I ran those knockers right through."
"Dude, look how tight her ass is. Would love to give that an ole north-southing."