As portrayed in Sex and the City, it is highly aggressive, fast-paced sex, resembling that performed by jack rabbits, or small dogs. It is essentially masterbating with a woman, chracterized by a pound-pound-pound-pound sequence. Men sometimes think it compensates for having a small penis or a partner with a particularly deep vagina, but really it's often painful for the woman.
"Ow, I'm still sore from that jack rabbit sex I had last night. I can hardly walk"